Of the options listed:
1. Zero Suit Samus (lots of interesting possibilities)
2. Rainbow Mika (she's just so rare)
3. Chun Li (more chun li is always good)
4. Tifa (more tifa is always good)
5. Filia (also pretty rare)
I'm a little surprised there are no Soul Calibur or Mortal Kombat characters. Or more Final Fantasy characters, for that matter. Or Tomb Raider. Or... I better stop before the list gets too ridiculous, lol
(Note: This list is in my order of preference)
Sophitia (SC)
Lara Croft (TR)
Lightning (FF 13)
Lulu (FF 10)
Cassie Cage (MK)
Yuna (FF 10, 10-2)
Taki (SC)
Cammy (SF)
Jacqui Briggs (MK)
Rikku (FF 10, 10-2)
Sonya Blade (MK)
Ivy (SC)
Paine (FF 10-2)
Kitana (MK)
Yuffie (FF 7)
If you consider adding any of the above characters, I'll redo my initial list. Note also that even if the character is from a deadly game like moral kombat, I personally don't care if the story lacks a fatality. That is, I want to see the characters, not necessarily the guro. (I like recurring characters anyway.)
Also, if you reconsider adding her, I also vote for adding Tekken's Julia Chang.