I think you shouldn't chose any of them. M&B (as far as I remember) use 1 (or 2?) cores/threads. AMD CPUs have a lot of threads (you can't call them cores, that's because of their architecture, but I won't tall about it. It's just geeky stuff). FX-6300 have 6 threads/3 modules), but they are not very strong (their single-thread performance is very poor). i3 Haswell (2 cores/4 threads) or i5 (4 cores/4 threads) would be a better option. I think that i5 is not necessary (but it's generally better for gaming).
For M&B I would go for something like this:
CPU: Intel i5 4590 or i5 4440 or i3 4330 or i3 4150 (all depends on your funds)
MOBO: Gigabyte GA-B85M-D3H
RAM: Kingston HyperX 4GB 1600MHz CL9
GPU: XFX Radeon R9 280 Double Dissipation or R9 270X - 1050M DD Boost Edition or MSI GTX 660 GAMING OC
HDD: WD Blue 1TB (WD10EZEX)
PSU: Thermaltake Smart SE Modular 530W or Thermaltake Smart 550W
CASE: Zalman Z3
ODD: LG GH24NSB0
i5 CPUs are generally for gaming, they have 4 cores/4 threads. i5 4590 is clocked 3.3GHz and up to 3.7GHz in Turbo, i5 4440 is clocked 3.1GHz and up to 3.3GHz in Turbo.
i3 CPUs are cheaper than i5, but have only 2 cores and 4 threads (that means there 2 cores are imitating 4 cores and OS thinks you have 4 cores - OS sees every thread no matter if virtual or actual as a core) and less cache. i3 4330 is clocked 3.5GHz and have 4mb cache, i3 4150 is clocked 3.5GHz too, but have 3mb cache.
R9 280 is the strongest of this three, but most expensive. This XFX version have very good cooling system (same as this R9 270X). GTX660 is the cheapest one and the weakest. Still it's better than GTX750.
This PC (version with R9 270X and i3 4330) costs around 665$, version with i5 4590 and R9 270X is 725$ and version with i5 4590 and R9 280 is around 800$ (prices from newegg).
I'm not native English speaker so sorry for any mistakes. If you have any questions I will try to answer them.