I am building a gaming/multitasking rig for a friend for about 600$. That leaves me about 150$ for a cpu, and I just can't decide whether to get something like an i3 or go with an amd cpu (FX-6200??). He's gonna play games like LoL, D3, SC2, so I don't think an integrated gpu is gonna be good enough. What cpu should I go for?
If you have a Micro Center nearby, you can get an i5-2500k for $160 which is about $60 less than it is online.
I would get that if its an option. You also get $50 off a motherboard when you buy a processor there, usually, so I would do that too if you are going there anyway.
If you can't do that, try to find one of the few i5-2400s left on the market, that should be slightly worse and under $200 even online. The i5-3450 is the new version of this, but it might be north of $200. It would also be fine if it isn't.