Gen III for me of course. I'm a "Hoennbaby" so yeah, you're damn right I love my trumpets. But their are some honorable mentions:
-Surf Music Gen II (God, that's a soothing theme. I remember when I got HG/SS after getting Surf and betting Morty. The first thing I did was run over to Route 42, hop on that water, and listen for a good 5 minutes or so.)
-Gen V Driftveil City B2/W2 (No sure if it's the same theme in B/W but damn that's a nice theme right there. Just very enjoyable.)
-Pokemon Colosseum [Evice Final Battle] (If you haven't heard that theme. GO listen to it NOW. It's probably the greatest major battle theme I've heard for Pokemon. Just majestic.) --- "RNG Gang." | OT: iSwagX | Slaking.
I play these games with the volume turned off. The music in Pokemon has never been the appealing aspect of the game. It just doesn't matter --- "Power of mind is infinite, while brawn is limited." Koichi Tohei