Hmmm...if I was to be a turtle it would probably be Michaelangelo. I'm not handy enough to be Donatello, angry enough to be Raphael, or leader-ish to be Leonardo.
Being Shredder for a while might be fun too. I dunno, some villains just have a certain cool mystique to them. I love capes! Of course, I'm smarter than the cartoon Shredder, so if I was him for a while we might not have any turtles afterwards!