Y'know, I've never quite understood the purpose of this question. To me, music is something that should vary depending on your mood or current task. For instance, I listen to classical at night (and right now, actually) to help me fall asleep, whereas I'll listen to dubstep during some form of physical activity. However, if I had to pick a favorite, it's most likely be trip-hop (here's an example:
http://www.youtube.com/watch?v=79_coGvHqvM) because of it's calming, yet energetic felling I get when listening to it. Though, these are just my thoughts.