Depends. The Q6600 was released in 2007, while the A6 was released in 2013. Despite being 6 years newer, the Q6600 and A6 have similar performance per clock, because AMD's core designs are so far behind Intel's. The Q6600 has 4 lower clocked cores to the A6's 2 higher clocked cores. The Q6600 can probably get relatively close (3.2-3.6ghz) to the A6's clockspeeds with a good overclocking motherboard, but those are becoming relatively rare. The A6 will draw a fraction of the power the Q6600 needs, so it will be a much cooler and quieter chip.
My opinion: At stock speeds, I'd probably stick with the A6. If you can overclock the Q6600, I'd give that chip the nod for raw performance, but it will be a hot and power hungry system.
What motherboard do you have for the Q6600?