Asus Still Top in Motherboard Sales; Gigabyte Close Behind
Gigabyte is right behind Asus in motherboard sales, although Asus still leads with profit margins due to the high-end segment.
While Asus is still the dominant seller of motherboards, Gigabyte is nearing it in terms of raw numbers. In Q1 2013, Asus sold 5.0 million motherboards, while Gigabyte was almost at that level with an impressive 4.9 million motherboards.
Nonetheless, Asus isn't doing badly. It has an advantage with buying the needed components, and Asus still leads the high-end market segment with which higher profit margins can be made in contrast to motherboards targeted to the OEM market.
Asus and Gigabyte combined shipped 45-47 percent of all motherboards through 2012. Following Asus and Gigabyte, ASRock managed to ship seven million units in 2012, MSI six million, and ECS, Biostar, Foxconn and a couple of other companies filled up the remainder.
Competition is heating up; let's see what Asus and Gigabyte have planned to take the crown for motherboard sales.

The first one did an admirable job overclocking my Q9550, the second one was sort of a mistake in the end as I didn't do my research on it and it did a moderately passable job overclocking my i5 2500K, and the last one did an excellent job replacing the second.
Not a terribly extensive experience, but between the two companies I've been mostly satisfied. Even the D2H was a decent motherboard, it just didn't have the features I needed and wasn't really designed for the things I was attempting to use it for.
However I do plan to seriously consider Asrock when I get around to replacing my core components in a few years. Their feature lists are massive and I ALMOST got one instead of the Asus.
I'm sure that has ASUS all torn up...