Get the i5, no competition. I am currently saving up so I can change the FX6100. Does the job for now, but there's no question, the i5 is the faster CPU.
Agreed. If youre building from scratch, the i5-3570K is the best of the bunch. The 3770K and 3930K are better performing but only by a tiny bit and definitely not enough to justify the extra $100-300 youd spend on them.