Another bet for it probably being Peacekeeper because it's got the BN duet thing going on (let's hope to the gods that the mike levels are right this time, as opposed to Leno), plus it's been released in the UK atm, so from a commercial point of view (assuming that the AMAs are probably broadcast in the UK; they are here) it's a surefire. They haven't had a chance to guage public reaction to a live performance of either Thrown Down or SYHA (you know, except for the rabid fans at the Soundstage, which isn't a very telling indicator for them), so they'll go with what they know.
Unfortunately.
But better Peacekeeper than SYW. I like both songs but the former translates much better live, I think most of us would agree.
But WHATEVER they sing - I just hope they look like they're enjoying it!!