Depends a lot on use case, certainly!

Also, do you like a “bottom up” or “top down” approach? Grabbing a raspberry pi and setting up a headless (no monitor) home server is a great bottom up way of getting familiar with things — learn to configure various services and whatnot from the command line. Or, just start with a user-friendly distro with a GUI you like, and gradually work your way up to looking under the hood.