I would say use any artistic performance skill combined with pretty much any athletic skill (maybe even running since that's about moving around). If it's just general dancing then music skills should probably be primary and something athletic complementing to offset the similar skill penalty. If you're trying to do something super flashy to impress you might want acrobatics as primary. If you've got a character or campaign where this comes up frequently, then probably a standard music specialization would be best. But always have a fallback plan, especially for simple dancing by folks just trying to fit in. Most social dancing is going to have a pretty generous difficulty modifier, so it won't take much skill just to avoid embarrassing yourself.
