if youre a power user satisfied with stock settings, i recommend the AMD FX 8320. But if youre an overclocker with an insatiable thirst for blazing speed, take a ride on the fast lane and overclock the AMD FX 6300.

The 8320 is marginally better. You can get decent overclocks from both (providing you don't have a duff chip).

Depending on your budget, it could possibly be better to not get either of them and take an Intel route.
From an upgrade point of view, the 8320 is pretty much the top of the line you would bother going for on the AM3+ chip. An 8350 is just a factory overclocked 8320 and all of the CPUs above the 8320 aren't worth the premium you pay for.
Take this from a current 8320 owner

P38a wrote if youre a power user satisfied with stock settings, i recommend the AMD FX 8320. But if youre an overclocker with an insatiable thirst for blazing speed, take a ride on the fast lane and overclock the AMD FX 6300.

Thank you AMD marketing team

Anyway, the 6300, 8350, 4300, etc. are all the same chip. They are binned according to how good the silicon is and modules of two cores are disabled accordingly. Eight-cores have all four modules enabled, six-cores have three, and so on. Disable a module on an 8320 and you'll have a 6300 that overclocks better. The 9590 is the best-binned chip.