It's a toss up between Sight and Touch. Toph is one of my all time favourite characters above all, not just in Avatar. I think it's so neat that she uses her bending to that advantage, and already earth bending would be my first choice. But sight. It would mean my dyslexia could be corrected and my focus enhanced. So many awesome things could come of this!
While I LOVE the idea of super hearing (it's like, my favorite super sense) in a practical sense, touch would help me out the most in my Massage Therapy career. I'd be able to feel the individual muscle fibers under the skin, all the knots and trigger points... Oh, please make this happen lol
I think I'll go with sight...though I'd like to keep my glasses (they are basically a part of my face, I've had them so long XD). But it would be great to have like binocular vision of some sort to pick out things at a distance, or be more perceptive to movement.