MSI boards are kind of finicky; you can overclock the *** out of them, but you have to get it right. 0.05 volt too little for the northbridge and it's not going to be stable. Nice boards for the hardcore users, but a pita for most. Asus is much the same (temperamental, as you say), but on top of that you're always better of making sure you have the latest BIOS.
Offcourse it all varies from board to board, but those are my global impressions as a brand.
Asus vs Asrock thing, well... Asrock was created by Asus to compete in the entry-level market, without risk of tarnishing their name by selling boards with cheap components. I would always suggest looking to MSI, Asus and Gigabyte (primarily) for high-end solutions first, untill Asrock establishes themselfs as reliable in the enthusiast market. But if Asrock starts selling expensive boards, they will presumably be using more expensive parts, making them a viable option.
Asrock is (or was) about price to performance, not quality and extensive BIOS.