This list is getting rather wildly outdated and so I have redone it better here:
This is quite an easy list as there is not much equipment, it is all quite similar in function and there is a large spread of power levels. Equipment is very hard to balance as it is brutal in non cube limited formats and far less powerful in any given constructed format. In any form of cube artifact removal is much more abundant and found in maindecks frequently. Also creatures are so powerful that tempo is of real importance in cube, both of which facts make equipment less powerful in cube. This is not to say that all equipment is weak as the early attempts at design were often over powered and not just for limited. What it does mean is that there is very sparse choice of top grade equipment that is almost always going to be a great bonus for your deck. If you do not get the choice equipment then you have to have your equipment fulfilling a specific role for the dregs to be viable.
9. Lightening Greaves
8. Loxodon Warhammer
6. Sword of War and Peace
5. Cranial Plating
3. Sword of Fire and Ice
1. Umezawa's Jitte
Starting with the cream there should be little argument as to my top two bits of equipment. The ordering of them however could be called into question and so I shall attempt to justify. Jitte is my number one choice as it and a guy win games and solve countless problems while Skullclamp needs a little more going on to become absurd. Jitte is actually slightly weaker tempo initially than the Sword of This and That cycle despite being cheaper to play. This is because it requires an attack to charge and offers no stats or protection without any charge. Once you get it on the go charging however it is very hard to be losing especially against a creature based deck. Any tempo you may have lost early in the game trying to get Jitte into play, equipped and charged will quickly return with interest. The reason Jitte is unpopular is also the reason it is so powerful and that is because it is near impossible to beat it when active if you are using guys. Against a Sword you can race and it is only difficult to block the dork with the sword, you can even get dorks which will hold off a Sworded up dork indefinitely. None of these things are possible against Jitte which can keep life stable, save counters to always have the biggest dork when required and use its removal to ensure blocking anywhere is really unfavourable. You either have to be stupidly far ahead, kill every single dork they have now and for the rest of time or kill the Jitte to beat it if you plan to win with dorks. In contrast the Jitte is not as good against most control decks than your average Sword and often too slow and useless against combo decks. Despite this is it still one of the best equips against those kinds of decks, it is equipment in general that is less exciting. With creature decks also being the bulk of archetypes Jitte will just auto win you an awful lot of games. It has the Strip Mine or Hymn to Tourach effect of a quick and unfair victory.
I much prefer the way that Skullclamp works and affects games to Jitte. It is more interesting to build around and has far more interesting choices when it comes to using it. It also rarely ends a game that was even in short order, it takes a while to build up an advantage using the Clamp. Clamp is also not as polarised as Jitte as to what it excels against. Beating control is its strongest matchup but it is good against agro and combo as well by virtue of being so cheap and easy to use. The few extra damage you can get in with it with mana you have spare against combo is often enough to win the game and is far more likely to be used and impact a game than more expensive equips. Skullclamp is a card not unlike Maze of Ith in that it can be very powerful if used correctly, or it can be misused to the point of throwing the match. It is oh so tempting to turn every one toughness dork you have into cards and then set to work chump blocking and so forth to turn your bigger dorks into yet more cards. Lots of cards is great but one must always be mindful of tempo. Trading your board position for card advantage is always a situational call to make and there are no hard rules about how to use Clamp most effectively. The best general advice I can offer is that when you are the aggressive player you should use it to add damage to attacks and provide a disincentive to removal on your best threats, when you are the control player you are more able to Clamp off a few weenies to fill up your hand and use the Clamp to stall efficiently with Clamperd chump blockers. The trickier bit of this is working out which player you actually are, especially as the mere presence of Skullclamp on the board might change you from the aggressor to the control player. Skullclamp is never a bad card to play if you have a high enough creature count, the cheaper the better. It is very difficult to beat in a war of attrition and has lots of great synergy in archetypes all over the cube. Equipment is generally there to give you reach, it also kind of increases your card quality by making each potential dork drawn to be far better. The drawback of the equipment is in loss of tempo and less smooth draws and curving out. The more reach and card quality you get from your equipment the more awkward it makes your draws and the bigger risk to savage tempo loss you get on the whole. Skullclamp is the exception to this rule as it offers the card quality and reach in a completely different way to all other playable equipment and is therefore able to be costed the same as the safest of equipment. A highly powerful and greatly undercosted equipment that is up there with Jitte on all accounts except that it doesn't just auto win games.
Now we move onto the next level of power for equipment which is a big step down from Jitte and Clamp but still very powerful in cube play. Sword of Fire and Ice is the best sword by quite a long way. Both effects are always good and generally able to work towards a common goal. No other sword really manages this. The protection colours are always good but obviously depend on matchup as to how good they are relative to the other options from Swords. A little bit clunky to get on line this poor mans Jitte does still get the job done and is a great thing to curve into as one of your last plays. An active Sword of Fire and Ice and some guys is usually enough to win most games.
Bonesplitter is one of the more underrated equipments as its impact is small compared to the other big names. As with assessing any magic card the first thing to do is look at the cost an equipments have two costs to consider. On both accounts Bonesplitter has a delightful cost, if you consider that it does about as much as a Sword if blocked yet it is 40% of the total mana. Splitter allows you to be very mana efficient and very aggressive, it is the best tempo equipment by quite a long way simply because you are never really losing additional tempo to any disruption or removal. In many ways it is a poor mans Rancor however it does have some synergy, safety and playability advantages over Rancor and does very much the same thing. I love it in white weenie, I think it is generally the best equipment you can play in red deck wins and I am a huge fan of it in blue critter decks which typically have lots of very lower power, and sometimes evasive, dorks kicking around. This does what you want equipment to do and it does it both safely and quickly which is more often what you want than sheer power of effect.
Cranial Plating is the first anomaly on the list as it is a very situational card. When in the right deck it is the best equipment however it is unplayable in most decks. There are only about four archetypes which can effectively use Plating and at present in my cube none of them can be drafted as so many of the required cards are in the B and C cubes. It is hard to rank a card that is incomparable in use to others, especially when it oscillates between the most powerful and unplayable. I have put it in at 5th because it has seen more play than those below it and for no other reason, it may soon however be overtaken in current playtime by Sword of War and Peace and Batterskull who are a bit too new to have meaningful statistics for.
Sword of War and Peace is the second best Sword in the cube but it is much closer to the third best than it is Fire and Ice in power. The proc is unpredictable and very narrow and while both damage and life are quite all round good things to have they are at complete cross purpose to one another making one half of the proc of very minor benefit every time. Often enough in cube this will be a must block as it easily kills in two hits against a fairly full hand and it is for this reason, all be it an unreliable one, that this is the number two choice of Sword. It has a touch of the Cranial Plating to it!
Batterskull is powerful and far less dangerous for tempo loss than a lot of equips and certainly all of the more expensive ones. Despite its relative safety it is still a very clunky card that is hard to play without access to a lot of mana (or a Stoneforge Mystic but more on that later...). This makes it very weak in many of the more aggressive decks which would be better of investing the initial mana in a dork or a planeswalker which then won't need further mana investments and will likely have more of an immediate impact on the board. What would you rather cast in in a beatdown deck: Baneslayer Angel/Wolfir Silverheart or Batterskull? For the mana you are going to be in a better position from making and equipping a Sword than you are from just flopping down the Batterskull. Where this does have application over other equipment is in control decks, particularly those with low creature counts. In such decks it is a recursive threat that can easily stabilize a board. Generally however control decks tend to play a higher count of threats thus not needing to opt for the recursion of Batterskull at a cost of lower power for the mana. Why play Batterskull and some generic control filler when you can load up on Wurmcoils, Titans and planeswalkers? Being a colourless threat is nice as he can be widely played and it does make him excel in artifact mana ramp decks where finding coloured mana or card advantage is tough but just having stupid amounts of colourless mana is no problem. As previously mentioned Stoneforge Mystic is highly abusive with Batterskull as it is one of the most playable high cost equips thus making the most mana saving on Stoneforge's second ability. Despite it being weak in aggressive decks as I previously mentioned the synergy with Stoneforge makes it a frequent player for white weenie decks.
Loxodon Warhammer is the honorary third Sword, it is clunkier and riskier but is more direct in purpose than the various non-red swords not in this list. The lifelink helps to stabilize for any tempo you might lose through getting the hammer equipped and the trample ensures you will be able to take full effect of the stats boost. When all you want is a way to make any given dork a serious threat then the Warhammer is about as good as you can get at the top end in terms of value. Certainly the other Swords do more and are a bit cheaper but what they do is random and situational, often enough a Vulshock Morningstar is doing the same. That is never the case with Warhammer which is very much in the 3rd rung of power in terms of cube equipment but gets the job done. It is the other end of the scale to Bonesplitter in that they are direct, no thrills equipment with good creature boosts for the mana. Splitter is the cheapest you can go and Warhammer is about as expensive as it is ever worth going in this kind of role. It is worth noting that all the Swords not featured in this list are powerful enough for the cube and would likely be played more than things like Lightening Greaves and Mortapod which are purely utility equipment, if it were not for the existence of Jitte, Warhammer and so forth. This is another way of saying that the cube only supports a bit of equipment in any given role. The ones dedicated to just beefing up your guys are more spoiled for choice and so make the top ten list not entirely reflective of absolute power level as some weaker equipment sees more play than the powerful but undesirable Swords.
Lightening Greaves are falling a little out of favour as there are better ways of doing one of Greaves jobs. Spellskite, Mother of Runes, Kira and so forth are much better ways of protecting your dorks which was often a reason to call on Greaves previously. It remains one of the best ways to give your dorks haste but at a cost of two for no immediate impact the loss of a proactive two drop is too much to make it viable in any weenie deck. A card and two mana is just a little on the steep side for most midrange decks to get excited about hasting up its dorks. The most common home for Greaves is in big artifact ramp decks where it vastly speeds up the effect of Metalworker into a threat while being of benefit as a protection for your few high vale threats. A fairly weak equipment that is quite unlike most of the others played in cube, both for its equip cost and its one off effect on dorks. You want it in play first not last as you do with something like a Sword so it is an awful late game top deck. When you really want haste and have no way to get Anger in the bin with mountains in play Greaves tends to be the best option (sometimes Concordant Crossroads is better in something like an elf deck). Certainly less powerful than all the Swords and probably a whole bunch of other equipment like Basalisk Collar, Grafted Wargear, Bonehoard, Manriki Gurasi and so forth yet still sees more play. Manriki might be the best equipment against other equipment but it is still worse than most artifact removal while Greaves is still a top rate haste giver.
Mortarpod is the final card to make the cut and is very similar to Greaves in being low power with niche applications. It is great for blue, white and green weenie decks that typically lack ways to deal with critters, especially those cheap annoying ones like Grim Lavamancer. It is also a great sacrifice outlet should you desire such a thing, which I find crops up surprisingly often in one way or another. Both Mortarpods costs are high given the power of the effects however the bonus germ does a vast amount to stem any tempo loss. I frequently find myself wanting another piece of equipment in a deck to make my Stoneforge stronger or because I am bad and am trying to get value out of a Puresteel Paladin... As filler equipment this is also very appealing as it is quite cheap, does not eat into your creature count and is kind of removal rather than typical equipment. The stats buff is rarely worth the mana and so like Clamp you are often condemning anything you equip to an early demise. While Greaves fills one niche well, Mortarpod occupies three niches a little tenuously; it is harmless filler equipment, it is a sacrifice outlet and it is a pinger.