Snowpoint city has the best IMO. It is the music that fits any city the best, and it's so tranquil and peaceful. Playing that while it's snowing outside the window is a feeling no other pokémon music can match. I can only really compare it to Ahto City in KOTOR, which also had exactly the right mood. Lavender and Village Bridge are also pretty nice.
The Kanto gym leader theme (FrLg) gets the position for best battle music for me. GSC/HGSS version is also very good, but FrLg's is best. Cynthia and Steven's themes also come close.
I felt that gen IV had the best music overall, I didn't like too much of gen III's soundtrack (inb4 trumpets), but it wasn't too bad.
The Kanto gym leader theme (FrLg) gets the position for best battle music for me. GSC/HGSS version is also very good, but FrLg's is best. Cynthia and Steven's themes also come close.
I felt that gen IV had the best music overall, I didn't like too much of gen III's soundtrack (inb4 trumpets), but it wasn't too bad.