It would help if you said what the rest of the system is going to be. The A6 is a big no no, AMD may say it's 2 cores but in reality it's a 1 and a half core, won't go into details with it.
If you're using a graphics card then get the pentium, at that clockspeed (3.1ghz) it's easily faster than the A8 in games with a seperate graphics card. The Pentium's integrated GPU is crap.
If you're NOT using a seperate graphics card and will be using the integrated GPU then go for the A8, but if you can go for the A10 as that has a better GPU on it.