Yeah, my vote is GT5. It's got a much much longer history and pedigree than the Halo series, and I'm betting there are a large number of people who'll be purchasing a PS3 in order to play GT5. To say nothing of those who already own PS3's. I know quite a few people who've been waiting, just for GT5. So, who knows.
I think though, more importantly, is that the GT series can appeal to pretty much everyone from the hardcore, down to someone who just wants to play around with the car they own in real life, whereas, Halo's following well, let's be honest, it kinda caters to FPS hogs (Nothing wrong with that!).
Even though I think GT will take it, I think they'll both sell like mad for certain. Oh and by the way, it's difficult to ascertain the actual sales #'s of GT5:Prologue, as it's also been available for purchase/DL via PSN, since launch day. Just an FYI.
