I am looking to upgrade my motherboard to support DDR3, USB 3.0, and socket AM3+ CPUs. I have used Gigabyte and ASRock motherboards without any serious issues. I have been a fan of AMD for years now and try to stick with them. Which motherboard manufacture(s) are the most Linux-friendly?
I think any manufacturer that supplies Linux drivers are OK. Personally, I would use Intel or Gigabyte. If you want complete hardware compatibility with Ubuntu, then you may want to check out the Ubuntu Hardware Support page.
ALWAYS do your research on the particular motherboard first. Some people say to use Gigabyte but they had an issue a few years back
I personally had an issue installing ubuntu 12.04 server on a Gigabyte ga-990fxa-ud3 to which their tech support said to install windows to fix my ethernet problem.
Google the motherboard you want and see if there are any issues. Even if a particular brand is said to be linux friendly, it doesn't matter because you are only getting one motherboard and it needs to work.
That is a somwhat subjective question. I normally dont use Linux on my Desktop, but I don't imagine you having problems with any manufacturer, excluding for specific models. Seeing as Asus has a lot of Ubuntu-based netbooks, I'd say they are very Linux-friendly, but if you don't have any issues with both Gigabyte and ASRock, then they should also be ok. But the best way is to search beforehand and get some feedback before buying a new motherboard.