You get one ability.

Envy's transformation ability from Fullmetal Alchemist. It would probably be the most useful ability next to teleportation or psychic powers (but if you could also transform into someone with those powers, then you would be pretty bad ass).

I'd have to go with Envy as well. I'm not personally an Envy fan, but I've always wanted the power to become someone else.

Ueki's power from law of Ueki! I would love to undo. Turn trash into trees and slam them in people's faces! If I could achieve level 2 I'd be the happiest camper too.

I too would have to say Envy's power, since I usually go with Mystique from the version of X-Men where she can also turn into a bird (or just in general), and Envy's power is an upgraded version of that (being able to transform into other people plus at least one other creature plus things like blade-arms). If I had the negative effects, like the screaming souls in my mind and the fixed, extremely-high density (although the density is kind of livable), I might choose... Hmm... I'm not sure. I was going to say a big-cat (lion or tiger) type Zoan fruit from One Piece, but checking the facts that arose since I stopped being able to read the series means they result in a violent nature, and that's not a good side effect. Therefore: Maybe Ryo-Oki's transformation ability from Tenchi Muyo (all the benefits of a small, adorable, energy-saving "cabbit" alternate form plus the ability to turn into something that can go very far very fast, which was half the point of the Zoan fruit above) or Ersza's "The Knight" armor/outfit switching ability from Fairy Tail (which would be both cool and useful for everyday life, and especially for cosplay if you put one or more costumes in the outfit-switching dimension). ...Interesting. All the powers I prefer that actually exist in anime as far as I can recall off the top of my head (as opposed ones I can't recall, and ones that aren't in anime) are shifter powers of one sort or another.

Speaking of Tenchi Muyo, I'd roll with whatever Ryoko's travel powers are. The whole shabang with the flying, teleporting, and phase shifting. All in one neat package. Funny thing is I'd be just as lazy as her in midair lol