RedHat till about version 9 (not Fedora 9, Fedora was exactly what made me look elsewhere). Debian after that.

Debian stable is, well, stable. It may lack some newest features, but its reliability is well worth it. Makes a pretty nice router or server, too. Thus, I have a single platform on all my computers regardless of their roles. Not quite good from the security point of view, but greatly relieves the pains of administration.