For linux, I've always recommended Debian. The testing and QA that goes into the package management is un-paralleled (IMO). It's *astounding* how easy it is to get packages on (and off) of a Debian machine, and it always Just Works. No muss, no fuss.

That being said, Debian isn't the fastest moving platform. I've recently experimented with Ubuntu linux. It's more or less a Debian fork, with tweaked priorities. I believe it's x86 only. It is desktop-focused, gnome-centric, and very polished. Seems a bit more simple than Debian. Releases are pre-scheduled every April and October, period.

So overall, I have a ton of experience with Debian. I recommened it heartily, but should note that I'm considering Ubuntu for my next build. (Whenever that might be...)