Amd fx 4100 or 13-2105 for gaming

Instead of the i3-2105, get the i3-2120. It's cheaper, and it has a higher base frequency. http://www.newegg.com/Product/Product.aspx?Item=N82E168...

I would prefer to get the i3 21xx for gaming over the AMD FX series CPU's. The FX 4100 is a 'quad core' CPU, but it's performance isn't all that great compared to Sandy Bridge.

by 13-2105 i think you mean i3-2105. and the i3 would do better, 95% of games cant use quad cores, and the i3 is faster making it a better choice for gaming. even though it is a dual core, it still performs as fast as the AMD quad. look at the benchmarks:
http://www.cpubenchmark.net/cpu_lookup.php?cpu=AMD+FX-4...

http://www.cpubenchmark.net/cpu.php?cpu=Intel+Core+i3-2...

AMD CPUs are more for multitasking for a cheap price. (many slow cores) if you are going to be gaming or running any other programs that need lots of CPU power, go Intel.(not as many cores but faster) if you need expensive but much faster multitasking, go Intel. (many fast cores)

Personally I would prefer to get an AMD CPU if I were on a tight budget and planned to do some casual video editing, photo editing, just because of the extra two cores. HOWEVER, I would prefer to get the Phenom II X4 965 over the FX4100.

When it comes to gaming, there's no doubt, go Intel.

thanks 2 all...

but 4 better gaming...whch i3 z gud..? i3-2105 or i3-2120
i3-2105 have 3000hd graphics but 3.1 ghz ..any way i use GPU..hd 6670..
i3-2120 hav 2000hd grap.. but 3.3 ghz..
i heard tht whn using GPU card.. onboard graphics will disable..!!

If you already have a Radeon HD6670, I would just ignore On-Board graphics  
On-Board really only matters if you don't plan on using a dedicated graphics card.

I would go with the i3 2120, it has a higher frequency than the i3 2105, which makes it just a little bit better for gaming.