Think Porsche (Seasonic) versus Yugo (Corsair). Peter Luger's Steakhouse vs McDonalds.
i'm not a big fan of corsair PSUs after my escapades with a half dozen AX860i's this past year. but you don't care about that. i do have the M12II and it's an incredible PSU for only being 80+ bronze. wouldn't even be a question for me with those two choices