Well I too vote for Ivy bridge. However don't think that Sandy Bridge is useless or anything. I believe at the same frequency (ghz) the Ivy bridge is better than the Sandy bridge. However at the same time I hear the Ivy bridge tends to heat up faster when the voltages are tinkered with due to the die size. On the other hand the Sandy bridge can take better overclocks compared to the Ivy Bridge. Either way I would go with the 3570k but if you are overclocking try to get a good cooler.
Edit: Just wanted to add that the Ivy Bridge CPUs generally consume less power under full load opposed to the Sandy bridge.
Most people would never know the difference between them. The 3570K is faster at the same clocks (5-7%), but it's not really enough to matter.
PCIe 3.0 and better power efficiency are what's really important about a 3570K (and the iGPU, if you ever have to use it. HD4000 is quite a bit better than HD3000).
The downside to the 3570K is exactly what socialfox said. When you add voltage to overclock, it gets very hot very quickly. Great cooling is a must for 4.5 and above OC's (better than a 212 Evo, for instance, when a 212 Evo will get you to 4.5, easily, with a 2500K)..