The FX 6100 Advantages
The FX-6100 performs 19% faster in multi-threaded tasks. In some applications, it is up to 47% faster.
The processor is unlocked. To get more performance from the microprocessor, it can be effortlessly overclocked.
The official price of the FX-6100 CPU is much lower than the price of the i3-2120 processor.
Intel Core i3-3220 advantages
In single-threaded applications, this CPU has 68% better performance.
The CPU is 11% faster when running memory-intensive tasks.
Graphics performance of the microprocessor is higher.
Power consumption of the processor is lower.
The CPU has 7% better price/performance ratio than the FX-6100 microprocessor
General benchmarks for both, from what I can gather.