Ton of comments, and I havent read them all, but I wanted to ask if you really meant popular or if you wanted something for a specific reason. Easy for new ppl to linux, good for desktops, etc etc.

I dont really use GUIs on linux, except for when I want to have a fancy pants riced network monitor type situation. I am a big fan of NixOS except for python Dev stuff. Big fan of being able to clone a machine or recover a machine with a single conf file.