What do you think is the best ability in the game?

Effect Spore is pretty useful, but it doesn't get much distribution. Similarly I like Flame Body and Static, since they take care of the status for me. Facing a Pokemon with such abilities pisses me off though.

multie scale is a really cool abillity that I just learned about when playing on poke showdown. It makes dragonite into a beaslty bulky sweeper. I also like serenegrace. hahaaa. paraflinch ftw

Serene Grace makes Togekiss epic, true. I think one of the really good ones is Speed Boost on Blaziken. Next time I play Black, I'm getting one of those :D

Trace is definitely an underrated ability. Porygon2 and a variety of other bulky Pokemon work great with it. With Trace they can freely come in on Pokemon carrying Flash Fire/Sap Sipper/type-absorbing abilities and then use them to their own advantage. Plus it adds a great element of surprise since many players forget about it. Definitely one of the more underrated ones. Another one is definitely Magic Bounce. While it's only carried on about three Pokemon, with the right prediction you can backfire all sorts of stuff on your opponent. Harry Potter and Pokemon crossing over. Never thought I'd see the day. <3;

And I'm really surprised no one has considered Tinted Lens. (I've skimmed over this thread so sorry if someone has actually mentioned it :p). It can turn a non-effective move into something that rips through everything. It gives underrated bug-types a niche and I honestly prefer it on Yanmega over Speed Boost. While I pretty much look at everything from a competitive aspect, I still think its a darn good ability in-game wise as well. And finally Simple is ridiculously overpowered. Don't believe me? Ozzy once swept me with a +4 Swoobat after about 3 Calm Minds. Talk about OP. ):

I would say Shed Skin and Wonder guard.

I can't say I've got one favourite ability, because I know 3 abilities that are pretty good. One of them is Moxie, really good for Fighting-types. Another one I like is Synchronise because it can screw the foe over. Also, a really good one in Generation V is Sturdy, because you cannot get knocked out in one hit. I don't really like Sturdy in Generations III and IV because it really only protects you from four moves (Guillotine, Horn Drill, Fissure and Sheer Cold), though.

-Tinted Lens is my favorite ability in the game. It allows pokemon whose shallow movepools could muster nearly nothing to do neutral against Steel-types, and allows even their stabs to do neutral. Examples include Yanmega, Venomoth, and Noctowl.

-Compound Eyes boosts accuracy by 30%. No, it's not the best, but boosting something like Sleep Powder to 97.5% and being faster than Breloom shouldn't be taken lightly.

Magic Guard, Regenerator, Multiscale, Wonder Guard, Imposter, and auto-weather are all in the running.

speed boost for sure(: gotta love taking the first turn.