for me it's slackware and debian; I've always loved slackware and I'm glad they're still going,
and I like the way everything works properly in debian stable; I have a friend who swears by Rock linux (you compiile everytihing from source like gentoo) but I haven't used it myself; one of my worst experiences with redhat enterprise server was trying to build a kernel with a specific patch level from a source rpm, if you've ever tried you'll know what I mean (messy post-install scripts...)