Not much of a gamer myself (and when I game I tend to do 4X or roguelikes), but I believe a Wonder Woman game would have the most marketing potential. There are a lot more female gamers out there than one thinks, Wonder Woman has the highest name recognition among non-comics fans save Batman and Superman, and her power set gives opportunities to a lot of different strategies for combat and conflict resolution.
"It's too bad she won't live! But then again, who does? - Gaff Blade Runner
"In a short time, this will be a long time ago." - Werner Slow West
"One of the biggest problems in the industry is apathy right now." - Dan Didio Co-Publisher of I Wonder Why That Is Comics
A Birds of Prey game could work very well. You could trade back and forth between Black Canary and Huntress depending on the mission. You could also have some hacking mini games with Oracle back at the Watchtower. Throw in some guest shots by Green Arrow in a Black Canary mission or Nightwing in a Huntress mission. It could be fantastic since both your leads or street level fighters.
I've seen a lot of suggestions for Green Arrow and I think that would work great.
Maybe a fighting game for the Green Lantern Corps similar to Naruto or Dragonball Z figting games.