I have to go with English on this one. Nothing gets a party started like Barbie Girl (Aqua) or It's My Life (Bon Jovi), and of course, the tearjerker The Reason (Hoobastank).
French and Japanese would tie for second place. I might not speak Japanese, but there are very few french songs I like so I guess they even out.
Btw, how awesome is this smiley ?