I've built about 90 PCs for customers (2003-present). About 10 of those were with MSI boards. Of those ten, one failed (MSI K8N Neo 2 or 4 Platinum without any sign of dodgy capacitors), another failed (MSI K9N Neo-F - bloaty capacitors), my parents' machine (MSI K9N Neo-F) has bloaty capacitors and can't take more than one memory module any more, and another Neo 2/4 Platinum has bloaty capacitors but hasn't shown any dodgy symptoms yet. The rest are ASUS boards, and one of those has failed (no bloaty capacitors).
I plan to warn the remaining customers using the MSI boards.
Someone mentioned ASUS having higher returns rates according to a website. I can't remember where I saw it, but I saw a survey of a (IIRC) tech forum in the last 3 years, and something like 90% of the forum who self-built were using ASUS boards. I realise the nature of percentages, but a survey of anything is more likely to be a better representation of the bigger picture if the survey is larger.
Personally I don't think much of ASUS's tech support, they seem to be as competent as the average broadband tech support person employed by a UK company (e.g. they're trained to read off cue sheets and they don't understand the nature of the questions they're asking, and furthermore they think they know what they're talking about). However I would be surprised if any mobo tech support department is significantly better.
I once had a chat with ABit's tech support and he was quite attentive, but it wasn't a very complex issue. I'm not sure if ABit is still around though...