Munn turning down Deadpool then taking this is...kinda baffling. As far as acting goes, my sole knowledge of Munn comes from this(I can't even name anything else she's been in, other than that show on G4), which, well, is not really something that allows her to show off if she can act or not. I've seen Baccarin in Firefly/Serenity, Spy, and Deadpool(and heard her voice acting on Justice League Unlimited), and thought she was thoroughly "average" in all of them(with a decent fight scene in Spy). So in terms of acting, I can't judge one as better than the other cause I simply haven't seen enough to comment.
As for looks though, well, I'm afraid Munn wins that one no fucking contest. I don't drool over Munn or anything, but Baccarin wouldn't even warrant a second glance if she passed me on the street.