Of your choices, it's pretty clear. Forget the 3770k as what it is strong at, really doesn't apply to gaming. Go for the 2500K if you plan to push an overclock as hard as you can, and go for the 3570k if you wish to take advantage of all the Ivy-Bridge features over Sandy, and intend to leave the CPU at stock or slightly overclocked settings.
Straight from the Wiki page for Ivy improvements:
Ivy Bridge feature improvements over Sandy Bridge include:[6][7]
Tri-gate transistor ("3-D") technology (up to 50% less power consumption at the same performance level as 2-D planar transistors).[8]
PCI Express 3.0 support.[9]
Max CPU multiplier of 63 (57 for Sandy Bridge).[10]
RAM support up to 2800 MT/s in 200 MHz increments.[10]
The built-in GPU will have 6 or 16 execution units (EUs), compared to Sandy Bridge's 6 or 12.[11]
Intel HD Graphics with DirectX 11, OpenGL 3.1, and OpenCL 1.1 support.[12] OpenGL 4.0 is supported with 9.17.10.2792 WHQL drivers[13][14][15] and later drivers.
A new random number generator and the RdRand instruction,[16] codenamed Bull Mountain.[17]
DDR3L and Configurable TDP for mobile processors.[18]
Multiple 4K video playback.
Intel Quick Sync Video version 2.[11]
And another little article on the topic:
http://www.pcmag.com/article2/0,2817,2405317,00.asp
At the end of the day, most of these changes are somewhat insignificant, nothing really groundbreaking until probably the launch of Intel's new lineup at least six months away.
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