i3 540 is older socket 1156 cpu, which you can overclock on some boards, but the motherboards are getting scarce. Don't get one of these for more than $50 us. Of the three, I like the 2120, which I use, but your selection will depend alot on price. Get the board, ram, and cpu all at the same time. You have to be able to test them together; don't buy them one at a time. I haven't used any of the amd cpus lately, so I can't comment on them. I'll find a benchmark for them if I can. http://www.cpubenchmark.net/
My recamend is Amd 4170 is $120.
4.3Ghz ,4Cores ,8Mb cache.
i3 3220 is $130 little higher ,3.3Ghz 1000Mhz slower than Amd 4170,2Cores Amd has 4cores,Intel has 3Mb L3cache Amd has 8Mb L3Cache 5mb higher than intel.