Bonnie it is then.

I think it could reasonably be either. Hell, you can always bring up the fact that Punisher or Captain America are 'humans with badass fighting skills' and I don't think we want to be running into either of those two any time soon.

We could have it that the item/artifact we steal to start this whole shindig off gives us super powers. Maybe that is why each of the two is so reluctant to give up the item and thus, stick together at the start.