Debian. For decades. My first installation was slack and from then until now has been a mix of more things than I care to list, but includes things like freebsd on a DEC multia, a sparcstation pizza box with a 2.6ish kernel maybe?, along with things like Ubuntu, suse, fedora, centos, gentoo, ive built from scratch, I ever remember the days of configuring x with fvwm95 because I thought it would be easier for my parents. I always go back to Debian. Though I'm happy with arch when I want something 'current'.