I would get the second one. The third one has hyperthreading, which is useless for games. There will be no real noticeable difference between 1333 Mhz RAM and 1600 Mhz RAM.
If possible, I would upgrade the GPU to the 560 ti. Keep in mind the computer is a small computer, so space will be an issue. Research to see what size video card you can get to fit into it.