While I'd be rooting for Powerglide, he stands no chance against a Decepticon warship all on his own. And I don't know much about Ghostbusters outside of the films. But from what I'm seeing, it doesn't seem like Wat has anything that he could do that could take down the Nemesis. Unless Wat has some crazy feat that I'm completely unaware of.
My vote goes to the Nemesis.