FX-6300 for sure.
There are THREE important features for gaming CPU's:
1. SINGLE CORE performance
2. Number of cores
(hyperthreaded dual-core CPU's are better than not-HT but not as good as true quad-core CPU's)
3. Overclocking potential
Dual-core CPU's can beat six-core CPU's in many games but only if they are a lot faster. If we look at Passmark for a rough estimate here's the results:
FX-6300:
https://www.cpubenchmark.net/cpu.php?cpu=AMD+FX-6300+Six-Core
A10-5800K:
https://www.cpubenchmark.net/cpu.php?cpu=AMD+A10-5800K+APU
Pentium G2120:
https://www.cpubenchmark.net/cpu.php?cpu=Intel+Pentium+G2120+%40+3.10GHz
Results?
Similar performance per core for all three, but the FX has SIX cores, the APU has FOUR cores and the Pentium only TWO cores (not hyperthreaded either).
Other:
APU has a GPU which serves no purpose with a dedicated card.
FX-6300 can't use all six cores for current gaming but we'll see some DX12 games use most of its performance eventually (thus it has roughly up to 3X the Pentium's performance if it could be used fully).
Pentium G2120 is a weak CPU for gaming.
In comparison the great i3-4370 is a dual-core CPU where the hyperthread can add up to roughly 40% more performance for some games and the single core performance is already 2211.
Summary:
Hope real data helps.
If possible do a light overclock to the FX-6300.