Definitely the 448 cores model. Only $10 more for 64 additional cores. Where else are you going to be able to invest $10 for that big of a return in performance? Especially gaming performance. For $10 more it is not a hard decision at all.
Ok, so the 560 ti w/ 448 core vs say an hd7850 w/ 1 or 2 gb of ram? I've done alittle reading and it seems the 7850 is definetly the favorite over the 560 ti