I can't even remember why I chose the Asus M3A78-EM (not the EMH which I think was the one that was defective).
Anyway, I just completed building the system right now but I have to play around with the BIOS once Windows is installed. I'm formating the HD right now and it might be a week (at the speed at which I work sometimes) to get all the latest drivers and verify all the BIOS settings.
It'll be a while before I can test anything. But, I can tell you it was a very painless install. I also find the Gigabyte GZ-X3 is very acceptable (actually pretty good) for a cheap case.
EDIT: (I don't want to add another post so I'll add it here) A lot of people like the Gigabyte model saying it has more
features than the Asus. As a matter of fact, you can find long threads
on that Gigabyte model if I remember correctly on avsforum, hardforum
and even a ton of reviews on newegg.
I just looked at the Asus USA website and there's a more complete
back panel for the M3A78-EM compared to the Pro. You have displayport
for the EM model even though it's the microATX form factor. And
apparently better overclocking ability.
Right now I seem to have a "mysterious issue" with the Asus M3A78-EM.
I flashed the BIOS to the latest one but I still seem to have like a
slight delay every time I click on something. And it says I have 1792MB
of "usable" RAM instead of 2GB. I read the voltage on OCZ RAM needs
to be adjusted on Asus motherboards so that may be it. But, I've returned
OCZ RAM for new ones in the past without a problem.
The models based on the 790G are more expensive and are not a significant
leap over the 780G. I read it's like the 780G but just overclocked.
I don't know if this is really the case but I prefer not having too much
heat.