The main differences are typically in the default paths, the package system, (although they're all pretty similar fundamentally) default software and whatever G

The main differences are typically in the default paths, the package system, (although they're all pretty similar fundamentally) default software and whatever GUIs they put on top of all of that. I don't think it's a waste of time to start with the GUIs. Sooner or later, if you're doing anything interesting, you'll need to drop to the terminal and config files. The config files might live somewhere slightly different, and work slightly differently with respect to versioning/updates. The implementation might vary, but what you gradually learn is primarily where to start digging, and that's transferrable between distros.