My personal top 6 would have to be:
1. Huntress (Helena Bertinelli)
2. Supergirl (Kara Zor-El and Linda Danvers)
3. X-23 (Laura Kinney)
4. The White Queen (Emma Frost)
5. Hawkgirl (Shayera Hol)
6. Majik (Illyana Rasputina) (most recent costume)
Honorable Mention: just about all of the X-Girls from the Ultimate X-Men continuity
Yes I know, I just listed pretty much all the big ones right there. Let me know if you agree or have your own list of favorites. They certainly do not have to be from DC or Marvel.