He's asking how do you prefer your headphones to sound. Since you listen to a range of things, you may not entirely be sure. That's fine. Nothing like trying out a lot of different cans to figure out what your preferences are. That's what I did (and continue to do). If you're really trying to get portable, there are some great, highly efficient, over-ear cans out there that don't require any amp at all to sound good. Start with the Logitech UE 6000, V-Moda M100, Sony MDR-1R, and Sennheiser Momentum. The Momentum is slightly out of your price range, but you should just hear it because it may make you want to up your budget that slight amount.
I'm really interested in those Momentum... I saw the other day one guy in the subway with them, should have asked him to try them, he talked me really well about them.