Re: The PCs are Villians - Which Villians?
Because they're not just heartless villains, I like the idea of using GRAB. However, they are a primarily female group and some male players get weirded out with the idea of playing a woman (even for a demo), so I'd add a few more male mercenary types to the team. Armadillo, Brainchild, and Thunderbolt II come to mind.
Also, there are a few games I've played that were long term villain games. One was Necessary Evil, but then again it's a villains fighting evil space invaders, so it's a bit different. Also, a Flash's rogues style villains game could work long term (which is also why I chose GRAB).