My first UN*X use was on SunOS. My first home UN*X was Coherent. My first regular-use system was Slackware Linux '92.
I've been running Debian since 1996. Used Ubuntu at work. Recently switched to Mint.
Developed and debugged server software on and for AIX, IRIX, HP-UX, SunOS/Solaris, and Linux.
Most comfortable on the command-line.