It's hard to say what game has the best music, because some times your not talking about a games music, but rather their licensing. GTA vice city and san andreas has awsome music, probably the best in video games. Again though this isnt the games music, they just bought the rights, or already owned them.
I would probably say off hand. Final fantasy X. An entire orchestra was sought after for this soundtrack. Fable, you can never go wrong with danny elfman. Finally, Halo had some of the finest battle music out there.
Tony Hawk underground2's soundtrack is the best ive heard in any game.
If you like trance, check out f-zero gx for the cube, as well as rouge agent. metal gears music is done by a famous movie composer.
classic music ahhhh u gotta love, the mario,zelda,double dragon series
heck what about the megaman series!!!!!! bubble mans theme song
check out the link for some classic sounds
http://www.vgmusic.com
The best music was definitely the aeon musci on Final Fantasy X.
Just whistling the tune to myself or listening to the sound bite version on my computer or thinking about it brings back nastalgia and watering of the eyes and occasionally some tears. This game is one of my favorite games and also my first Final Fantasy game.