Ah, the age old question that I hate being asked, since I'm never sure how to respond.
I'm more about individual songs than a particular music genre.
However, music I tend to like the most songs from is Soft Rock / Contemporary / whatever-that-kind-of-music-is called, so if listening to the radio, it tends to be a station that plays that type of music. I don't listen to the radio often, though; I prefer listening to stuff on my own playlist.
Other music I really enjoy comes from these genres: Video game, Christian (Contemporary), and Orchestrated/Instrumental (I guess Classical could be included?). I suppose "Soundtracks" would fit under these? Some rock, pop, and country is okay, but it tends to be the songs that cross over into the soft rock genre.
I don't like Rap, Hip Hop, R&B, and that loud metal rock or whatever where all they do is scream and roar. I also hate it when a song has a really cool beat/melody, but the lyrics are awful (this includes any profanities, too). :(
If I had to give a simple definition of what music I like, I'd say "pretty" music. Vague, open-ended, and subjective, but meh. If a song has piano, strings, and/or electric guitar, I'll probably like it. Wind instruments are good, too. All that stuff's usually "pretty," as I define it. I'm not big on acoustic guitar, though.