There is little comparison between the two. GTAV is a marvel. in every sense. A marvel. I just can't wait to see this marvel on PC and next-gen.
AC is also a great achievement, had it not been the fifth entry of the game, then I would've said that AC and GTA kickass together. But AC got the same old crappy story, that attempts to hijack every single historic era. Whereas GTAV develops story of its own, and make you fall in love with it.
My vote: GTAV
only console gamers should be allowed to take part in this poll. AC is a beauty (indeed), but those who say that, haven't flown a military chopper over the hill with the river slithering down below, and the sun gleaming straight ahead.
Only yesterday I played GTAV and switched to Trevor. man! He was riding that crappy scooter in the dusk. Just wow.