My choice would also be the 3570K w/Z77 or better MB.
Your gaming is much more dependent on the GPU, Not a big difference, with identical GPUs between the 3 CPUs.
i5-3750 is about 10->15% better Overall than the i5-2500K. The only advantage that the i5-2500K has over the i5-3750 is that the i5-2500K is easier to Overclock.
The newer Z77 Motherboards are much better than the older SB MBs (ie z68's) in that they have better SATA III support, Native USB3 support and Pci-e 3.0 (not a biggy currently but will have more impact in the near future. This is The biggest reason, Not the diff in CPUs, that I recommend the Intel build over the AMD - Better overall MB performance. Intel seems to improve the drivers on a more frequent bases for their MB chipsets.