Linux has many options - freedom to choose, which is great but beginner gets overwhelmed with the choices. There are over 100 Linux flavors to choose from but even if you focus on say first 10-20 each comes with many different desktop and windows managers such as KDE, Gnome, Mate, Cinnamon, Xfce...
If your computers are older & slower, you want to choose lighter desktop manager such as Xfce that is lighter on resources. If say Mint Xfce is still to slow and lagy, check out Antix full:
http://download.tuxfamily.org/antix/docs-antiX-17/FAQ/index.html
I'm running it on one slow, 32 bit netbook and it runs great