3570K. between those two processors, the i5 will beat the 6100 in every single gaming title (and more).
The i5's superior IPC will outweigh the AMD's additional 2 cores.
were you to go for a 6300, I'd have still told you that 3570K was superior though would have voted for the 6300 b'coz it is a great gaming chip. Better than 6100 (which would require a rather high OC and therefore cooling to match up).
a 6300 will handle the very best gpu's out there pretty well. might need a little OC but will drive a 7970 too. It's that good value for money.
^ +1 for the FX 6300, if your a bit tight on cash, but if you have the extra $80, then get the i5
The 6300 is sufficient for handling mid to high end graphic cards, and in multi threaded software that can take advantage of all 6 cores, it hangs right in there with the i5's for $80 less. Now that's what you call value for money
Very good chip for video conversion/editing, heavy multitasking and stuff
Here's a link to a comparison of teh FX 6300 and the i5-3570K. http://www.anandtech.com/bench/Product/701?vs=699&i=499... One important thing to keep in mind is to factor in prices and you get the right chip for what you do in your system, not what someone else trying to push BF3 at some insane resolution with 5 monitors while editing a video in the background.