Personally,I strongly prefer Linux.
Lightweight, reliable, and you get to dirty up your hands with tech work. Also, It's free and doesn't beg you to upgrade. It has fairly good driver database, only real pain is that alot of stuff won't work with it, but on the upside all that stuff is usually supported on a user level. For instance, my phone didn't have any stuff to sync to Linux with (well, except as a mass storage device) but some poking around on the forums and now it syncs perfectly.
Windows is fine, too, I just hate that they try to force you to upgrade, making it seem like your computer won't work if you don't. I understand you can't keep supporting legacy hardware, but the way they push upgrading makes it seem like after a certain date your computer won't function.
MacOS is pretty cool, too. Just WAAAY to expensive for what you get. Honestly, I think Apple has turned away from it's original values. Before, Apple computers were fairly cheap(like, the 80s). They weren't the cheapest, but hell they weren't 3-4 times the price of a PC with half the specs.
--Ryan