Intel Core i5-3330 3.0GHz Quad-Core or AMD FX-6300 3.5GHz 6-Core
Which one is better for gaming?
The i5 3330 is better at stock clocks. Overclocked to 4.5ghz, FX 6300 would probably match if not come out just slightly ahead in higher threaded games. An FX 6350, which is the same basic chip, @ 4.5ghz, is just under a 3570k at stock. The benefit of the FX 6300 is the significant price difference, allowing for more $$ to be put into a better GPU.
If you are looking at locked i5's, you would probably be better off going with an i5 4xxx series chip. They are not really priced all that much higher now.
This depends entirely on what games you play and how many cores they will use.
The best overclocked i3 cannot keep up with a stock FX-6300 in multicore optimized games like Crysis 3, Arma, Metro, Battlefield.
But in older games that only use 2 cores, the fx-6300 cannot keep up with the i3 because of intel's far superior per-core IPC.