The Gigabyte GA-MA78GM seems like a safer bet to me. I love ASUS, although the ASUS M3A seems to have drivers issue, at least from the customers point of view. Plus, the Gigabyte offers a newer chipset.
Questions to ask when ever you're buying a motherboard, apart from the series (AMD vs Intel) :
- Are you interested in overclocking your PC?
- Do you want Wifi or dual LANs included?
- Do you want SLI or Crossfire?
So as you can see, it all depends on the features you want included with your motherboard. The more feature you're looking for, the more expensive it will cost.