refllect :
I prefer an i3 over a FX-6300 for much better single core performance. Most games don't require more than 2 threads so the i3 will perform better for those. Of games that require more the i3's hyperthreading handles them well enough so that the fx-6300 has only a marginal advantage. Plus if you're upgrading with an AM3+ motherboard, your only option is a FX-8300 which doesn't give much of a performance boost. FX-9xxx are really expensive. If you go with the i3, the option to upgrade to an i5 is cheap and offers a major boost in gaming performance.
i3 is a clear winner to me unless you are running multi-threaded applications instead of gaming and you don't intend to upgrade.
There are a few older game engines that can favour the stronger individual threads of the i3 . Most are DX9
Everyone else is better with the FX 6300 . The newer , graphically intensive game engines all multithread very well . BF3 , Crysis 3 etc are the future so buying an i3 makes no sense
It makes even less sense when you consider socket 1155 is already obsolete
and that there is another entire generation of cpu's coming from AMD that will drop straight in to an AM3+ motherboard