I thought about this awhile back!
I really liked "lupin", "mister", and "wanna". "Jumping" was a good song but I liked the cheerleader version way better than the original. They did touch on a hip hop theme if you've seen their dance for "Burn" and I liked that alot! And they were REALLY cute in their "2me" vid too.
The dark/chic/mysterious vibe was a good route for them, but they fit more naturally in cuter themes I feel.
I am all for sexiness however! lol To actually answer the question though, I think a latin theme would be great. Something bossa nova, yeah?