I've usually stuck to 'main stream' Linux distributions - such as Redhat or Debian, and avoided the (what appear to be) offshoots - such as Knoppix, ubuntu and the such.
Now, I use distros like Knoppix (an excellent Live CD that can save you ass when a system folds!), but I've never looked at desktop / server distributions.
Last Friday (yes, Friday the 13th) I was discussing distributions, and was advised to check out ubuntu - a distribution that is heavy based on Debian, but a LOT easier to install!
I've since downloaded and installed the i386 build on my laptop (overwriting the previous Debian install), and now only need to spend some time configuring my apps (Borland Kylix) and my Belkin 54Mbps PCMCIA Card. (More on this later!). So far, my thoughts are positive - ubuntu is an excellent low weight distribution (its shipped on a SINGLE CD-ROM!), it's stable (like Debian) and quick to install (unlike Debian!).
I'm also planning on installing the x64 build onto my desktop. Maybe if I get a chance I'll replace my Redhat Fedora Core dev box with ubuntu.