I started with the original Slackware on floppies. I'm running SUSE 11.1 on my personal laptop. SUSE 11.2 on my FreeRadius servers. I think I still have Fedora on one or two legacy boxes. And the old 2.4.19 kernel on an ARM appliance.
But, whatever I pick, and works for the need, I stick with it. I'm not big on updates and moving to the newest.
I have work to do, and don't have time to be installing and figuring out new distros.
/johnny
I'm biased toward
Linux from Scratch. I use that a starting point for my homegrown, heavily-customized system. Every single component is built from source (Acrobat Reader and Flash are among the few exceptions) and tweaked for my CPU. Plus the kernel is light, comprised of only the features and drivers that I have on my platform.