Core 2 is old and pretty defunct. It all depends on your budget, what GPU you get, what resolution you'll be gaming at, and what games you play. The typical go to standard is the i5.
YUP Core 2 duo is what 5 or 6 generations old for intel. I5 is the best for gaming, I7 is equally as good but has hyper threading and games don't take advantage of it so the extra for the I7 is wasted money if all it's for is gaming.