speaking of overclockability, I remember this one ECS board that actually WON as the most overclockable board of its time. It wasn't even too long ago. So ECS is not a gaurenteed non OC. Then again, most ECS boards I had wouldn't OC at all. (and that board was a very expensive OC minded one).
I don't know why you brought up 300$ boards. A similar chipset / features board would only be a few (10 or 20) dollars difference between different brands. The 300$ boards use more expensive chipsets and more expensive features (on board wifi, etc).
And yes, you WILL have flaky boards from ALL manufacturers... I am just saying that my experience I had MORE flakiness from abit and ECS, and the least flakiness from ASUS and Gigaybte and MSI. And as far as I am concerned, a single RMA, or a few extra hours of figuring out the exact WAY in which the board flakes and working around them is not worth 10 or 20$.
I would take an ECS board in a heartbeat if it was 50$ less, because for that much money it IS worth my time to mess with.
Ofcourse INDIVIDUAL boards matter too.. if you hear board X from ASUS is extremely flaky and board Y from ECS is rock solid, then board Y is the obvious choice. But if you haven't found much on a per item research, a safer choice would be a top tier manufacturer.
I also don't recommend potentially more difficult to work with boards to people because I don't know how comfortable they are with computers and with messing with things. Last thing I wanna do is give advice to someone that will end up with them unable to finish their build. (not EVERYONE can find workarounds like we can

)
Lastly... I would rate ASUS as 2/5 stars, gigabyte and MSI as 1.5/5 stars (they loose half a point for their horrible engrish). And most other manufactureres between 0 and -3 out of 5 stars.
Don't EXPECT quality and stability from the computer world. Expect bugs, work arounds, and don't even bother trying to do ANYTHING before updating to the latest version (bios, OS, software, drivers, etc).