My top five traits
Inspiring Leader - Iron Kaiser
Yes, it's a shameless plug, but I wouldn't have made it if I didn't like it. Anyway, there are a couple of things that I really like about this trait. For one, it's a trait that is balanced without having to make it rare. If your hero doesn't fight with other heroes, is too lightly armored for the ensuing enemy attention, or focuses exclusively on powering himself up, then he won't -want- this trait. But if you're creating a good front-line, team-based character, then you'll definitely want the trait. Also, "Inspiring Leader" changes the battlefield in a novel way. The way the trait powers up your allies while simultaneously making your "Inspiring Leader" the center of the enemy's attention is pretty neat, and causes both sides to make some interesting tactical decisions. Also, I have a preference for passive abilities, and this is a really good one along that vein. I guess I have a hard time critically evaluating my own trait, but I'd say it's a really nice one.
Shape-shifting - nitey47
I really like this trait for the tactical variance that it provides. It would be a great trait for grunt-level units to adapt to the tactical conflicts that confront them. Nitey47 already provided some examples, but another good one would be slow, heavily armored swordsmen transforming into a fast band of crows, losing their pure strength but gaining range and speed. I also really like the trait because it requires thought before you use it. Since it can only be used once per battle, it would be easy for the enemy to trick you into shape-shifting, thus depriving you of the heavy swordsmen or archers that you may need later in the battle.
Blooded - Tydorius
I'm unable to read all of the lore written for the trait, but that's okay, since the lore isn't what earns this trait a top-five spot. The effects of "Blooded" come from classic RPG gameplay, and it would be a shame not to see something like this in the game. Again, I can see how this would change up the tactical battle situation, as the "Blooded" hero desperately tries to keep the trait from activating before facing that one giant, menacing badguy on the other end of the field (and of course, the bad guys are trying to activate your Blooded ASAP).
Mana Leech - Tiavals
I'm a huge fan of judo-esque powers. Sapping the enemy's health, stealing their power, snatching their mana- I love this kind of stuff. So Mana Leech is a really neat power, right up my alley. I'd appreciate a little bit of tweaking so that the mana can only be gained by non-magic attacks. This would have the effect of giving the trait an interesting spin by requiring a caster to step out of their casting role. I imagine that "Mana Leech's" most important use would be when the hero is running low on mana and needing the mana in order to cast power. So, the hero has to use bow or sword to gain the mana. Thus, it's a trait that's not terribly helpful for heroes who don't really use mana or for heroes who attack exclusively as casters. The percentages also might need some tweaking. But all in all, this is a really neat trait.
Unstable Magic - Vinco
I like the idea of pushing magic to its limits and fighting with "Unstable Magic." It would be kind of like going to battle with an experimental war machine: you just don't know what you're going to get. When you try casting that fireball, you don't know if you're going to get the regular fireball, a fizzled-out spark, or a burning meteor twice as powerful as the normal fireball. Plus, it's a guaranteed story-maker. Somebody, somewhere will have a story about how he lost all of his men to this evil monster, had only his caster left (with 1HP), and his only hope for victory was casting a fireball in hopes of getting that superball. I'm not so sure that the boost mechanic and the specific percentages are perfect, but the underlying concept is awesome.
Some Honorable Mentions
Equipment-Linked Traits - Lomonion Agarwaen
A very neat idea that definitely deserves to be in the game. If the traits are tied directly to the equipment, then it could give the player a fun, unique dilemma between two different weapons - one weapon statistically better, but the other providing an enticing trait. However, this is more of an broad idea than a specific trait, and so I'm afraid that it's not really eligible for the contest.
Black Market Merchant - Trojasmic
It's a solid trait idea, and I can't help but appreciate someone who foregoes Xtreme combat traits in favor of a good passive economic trait. I hope we see traits like this in the actual game.
I'm sure I missed somebody, but at least for right now, these are my top picks.