I have five favourites I'll give my favourite of each track of each ost...
Skies of Arcadia (Little Jack Ship) http://www.youtube.com/watch?v=LFcH84oNU6s
Chrono Trigger (Frog's Theme) http://www.youtube.com/watch?v=fMzkUriqXvs
999: 9 Doors, 9 Persons, 9 hours (Morphogenetic Sorrow) http://www.youtube.com/watch?v=WjNi14fKSow
Lost Odyssey (Neverending Journey) http://www.youtube.com/watch?v=135Gltfkxeo
We Love Katamari (Kuru Kuru Rock) http://www.youtube.com/watch?v=fn59_HopFRc&feature=related
Former something....