i3 wins in most games at stock, but with a healthy overclock, the FX is still a respectable chip and will play most games smoothly. There are a few games that are very single-thread limited, such as Arma3, which will run considerably better on an i3 than even an FX-9590, but you'll see better average framerates with an FX (by a little) in games that are well-threaded such as the Battlefield series. The i3's performance in games is more consistent, really, which is why I give it the nod, but the FX will be a lot better in anything that can load up all of its cores, such as decompression and encoding that aren't GPU accelerated, which is less and less common as time goes on.
More importantly, the i3 has the drop-in upgrade of an i5 or i7 available, while AM3+ is a dead-end, and will draw 1/3 to 1/2 of the power while performing similarly or better in games.