All-time top four:
Tallon Overworld from Metroid Prime
Time's Scar from Chrono Cross
Gusty Garden Galaxy from Super Mario Galaxy
Brinstar from Metroid
Best composers:
Koji Kondo (Mario and Zelda mostly)
Motoi Sakuraba (Tales of, Mario sports games*, a lot of other RPGs)
Yasunori Mitsuda (Chrono series)
Kenji Yamamoto (Super Metroid, Metroid Prime series)
Yuka Tsujiyoko (Fire Emblem, Paper Mario)
*Do not underestimate! I think his Mario Tennis 64 match themes and Mario Golf 64 course themes exceed his RPG work.