My favorite genre for just chillin' or studying is postrock, but my favorite song is probably Black Tables by Other Lives.
I'm a mad fan of chiptunes, so I'd go with that. I've already messed around with FamiTracker, which specializes in making chiptunes, so I'm sorta set?
I've already made a few using my DS, so all I have to do is figure out how to actually use FamiTracker effectively.