SUSE Linux, back in the 1990s. Because you could buy it for cheap, and you got not only the huge stack of floppy disks to install it from, but also a set of thick fat detailed handbooks (these things made from paper full of pictures and letters and glued together, like your grandparents may have had). I spent many nights with them books instead of my wife…
It was a bear to install and terribly complicated to configure back then; at least for me. But in the end, I had a nice server running well for a while.
Practice, practice, practice.