I like both for different reasons. Fallout 2 is still the best though.
I got more immersed into Fallout 3 for some reason, it felt much more like "you against the world" for me, and i liked that aspect. I also liked the story a bit more, not the characters, but the overall story. Got tired of the green tint and similar locations, so the change of setting in New Vegas was greatly appreciated. As well as the few gameplay tweaks that added to a more accesible experience. They are different games and thankfully we have both, New Vegas just takes it up a notch with better writing, better characters, and gameplay tweaks.
What setting you like the most is enough to make you prefer one game over the other though. NV isnt such a big departure from F3 at all when you look it from a distance.
edit: As for the music, i love both, but the limited tracklist is actually part of what "keeps me away" from another playthrough in the end, i just got really tired of them. My next playthrough (wich will include the DLC released so far) im probably going 0 radio. Or maybe some mod that lets me build my own soundtrack, one that fits the game of course