Of the two options listed, the first one is the better choice.
FX-8150 is pretty much a waste of time when it comes to gaming, while the A6 system is option, it's already a dead end option, as the next series of APU's will be moved to the new FM2 socket
I woud therefore be more inclined to point you toward an AM3+ based system with something like an Phenom II X4-965 for the processor. As it stands now, we may see one more generation of CPU's for the AM3+ before a new socket is released... but only time will tell.
EDIT: BTW... I played the Diablo III BETA in the final week it was online on an A8-3870K with the integrated GPU for the graphics. It handled it surprisingly well, running at 1280x1024 with all in game settings maxed for quality, it dropped to 15fps once durring the Jar of Souls fight & dipped to 23fps durring the Skeleton King fight, but other than that averaged about 34fps.