In most cases you will not be able to tell the difference.
In some games the i5-3330 will be far better, as a lot of games aren't optimized for 8-cores.
In the end you will not go wrong with either and it pretty much comes down to MOBO selection, power consumption and if you want to overclock. Because you could squeeze some more performance out of the FX 8320 as long as your able to keep it cool.
I myself would possibly get the FX 8320 actually as many of the upcoming titles will support 8-cores, just as the Xbox One and the PS4 features of course also the possiblity to overclock is a great thing.