Phenom if you're gaming. It depends on what you're prepared to spend, as well. I went with the top-notch 965, which is X4 (quad core) and 3.4GHz, but you can go with the X2 555 for half the price. It's a X2-3.2GHz. I really suggest at least a X4 - 3GHz, though. You're better of future proofing with CPUs, because they're the hardest component to upgrade.