The Athlon x4 635 would be the best then the i3 the Phenom x 2 would be far better if you can unlock 2 extra cores but its a gamble other wise it would be the worse. There is not a huge difference between any of them and they are all a good match with the 5770. Away from gaming I would still rate them the same as above but the 4 cores would be of even more benefit. The only reason to consider the i3 would be it should overclock further and the only reason to get the Phenom x 2 is to unlock 4 cores (which is the option I went with and it worked).