I really like Frog's Theme sometimes, and really get annoyed at it other times. If I listen to it for long the tone of the melody gets very grating. Everything else about the piece is very good though.

My favorite Chrono Trigger song is probably Zeal, though that might be affected by the overall environment during that part of the game, which is probably the best in the game. As stand-alone songs, I might like Robo's Theme or 600 AD better.