OpenSuse (back then the “normal” one, then Leap and now the rolling release Tumbleweed). It just works really well and keeps on trucking. Updated my old machine for ten years through all the openSuse releases without reinstalling. The repositories are very well kept in order and the build service easily provides anything I might find lacking.

Also, I quite like using Yast for system administration. There are many areas that I rarely touch and having a GUI available is super helpful.