LogFAQs > #970326801

One choice, gun to my head, I'd probably have to say Space Dance. I like the song, the characters, the silly engrish.

Some of my favorites from each game:
GBA: Rhythm Epilation, Toss Boys, Space Dance, Power Calligraphy, the one with the bouncing balls which I can't remember the name of.
DS: Munchy Monk 2, Karate Man, Rhythm Rally, Spashdown, Moai Doo-Wop (yes, really)
Fever: Ringside, Bossa Nova, Flipper Flop, Board Meeting, Cheer Readers
Megamix: we don't talk about this game

I kinda want to gush about that GBA game for a minute. It's a shame it never released outside Japan, since it honestly might be the best one. I can (and have) gone from a fresh save to all perfects in a single sitting. Partly because it's way easier than the other games and partly because it's just so fun to play.