For a long time, my favorite was Robo's theme. It's so fun. ^_^
Then for awhile, Frog's theme. Totally heroic!
Then of course, Schala's theme. Peaceful but regal. I always imagine the bells at the beginning as being little bells on her royal gown or something...and it's the sound of her approaching. ^_^
But lately, with me possibly getting married in the next year or 2, love is on my mind...so Marle's Theme it is.
(The full version, "To Good Friends," not the musicbox-only version.)