Redneck5439 :
Eliasand :
Those 2 perform very similar in today's games. While you may get more FPS with the i3 on single-threaded games like CS:GO, the FX6300 is a bit better in new AAA games like Fallout 4.
I would recommend the i3 because of it's upgrade path. If you buy the i3 now with a decent motherboard, you just have to buy a new CPU in the future, for example an i5-6600k.
The FX is old and the AM3+ socket won't bring out any new processors, so when you want to upgrade, you have to buy a whole new system.
Keep in mind the "upgrade path" for the i3 6100 is always going to be Skylake CPUs. Once Kaby Lake comes out next year Skylake will be a dead socket as well. You will not be able to put a Kaby Lake CPU in a Skylake motherboard. Therefore if you want to again upgrade to the newest arch (a year or two down the road) when you do upgrade (and eventually we all upgrade) you will have to get a new motherboard and processor.
Considering that Kaby Lake is just a Skylake Refresh, I would imagine they would be compatible with existing LGA 1151 boards, unless Intel has issued a statement saying they are not. 2017's Cannonlake might not work with LGA 1151. The i3 is still a strong performer, and even in newer games, it's still outperforming the FX CPUs. Fallout 4 isn't a good example in favour of the FX CPUs, even the FX 9590 barely keeps up with a Haswell i3 in that game, a Skylake i3 would beat anything in AMD's current lineup for Fallout 4.
Games are getting more multithreaded, but AMD has fallen so far behind now, that they simply aren't competitive on anything except price. DirectX 12 might breathe some more life in to the old FX CPUs, but by the time it becomes mainstream, Zen is going to be out, and the FX CPUs are going to be 4 years old at minimum. I wouldn't buy an FX CPU at this point unless I literally couldn't afford anything else. Between the age of the CPU and lack of modern chipset features on the AMD platform, I don't see them lasting all that long, they're really a great choice if you're looking to build a system you want to keep long term and not have to upgrade in a couple of years.