If you can avoid it, forget RMA'ing anything.
Never buy refurb or open box either, companies do very little testing on them.
The dotcom I worked at, as an exclusive importer of some items we had to deal with RMA's on some items.
It was told to customers it could take 2 weeks, to 6 months to RMA a DVD rom. At the time, because prices on them were falling so fast, you could spend $200 on a dvd rom, and by the time you got it back, it could be only worth $50. You were also not guaranteed a new replacement.
My last RMA with Asus was also a nightmare (still like them, but jeez!). The Maximus Gene board I bought open box worked fine out of the box but about 2 months later the PCI-E port failed. I sent it in, sat on a shelf for 2 days, then 2 days diagnostic, then they sent another to me express or 2 day. Overall, not bad, until I got it open and found that the memory slots were all bad and the board wouldn't even boot because of it. Absolutely zero QA was done. When the survey came regarding support, I trashed them for it.
One customers refurbed $2000 Sony laptop had a bad network port. Sony is a whole bag of worms anyhow... Great laptops, terrible support. I have yet to see a good Sony refurb.
Another customer... Every 6 months she was sending it in for a drive replacement. Always fast, and always wiped. After 2 years and the third or 4th drive, she finally replaced the system. While hers wasn't one, like Sony, every HP refurb I have seen has had problems. HP is always good for support when you do have issues though, it just stinks you need them so much.
Good ones to deal with...
Apple Refurbs I have heard good things from them, and never a complaint.
XFX, spent a long time with me in email diagnosing my video card, and offering to run a full diagnostic if I sent it in and offerred some alternative options as well. In the end, it wasn't the card that was faulty and I still use it.
Western Digital, I only had dealings with them many years ago, but every time, the drive was replaced with newer and bigger, and very, very fast with no questions. I don't deal with them anymore after having so many go bad though, because not having to RMA, is better than any RMA experience.