Right now, macOS. Switched to it when I started uni and I'm never going back to Windows. The main reasons are:
unix based
generally easier to manage software
the OS itself has most of the basic utilities already packed in and most of them with the right features. I rarely felt the need to install new software to cover lacking parts.
Also, generally stuff is packed fairly well, with care for user experience.
I will say, I'm dipping my feets in linux as well, and it looks like a lot of distro now are mature and accessible. If I ever were to buy a second pc I would seriously consider the penguin.
The Chameleon and the Thousand faces were some of my favourites in concept because of their flexibility, though I never had a chance to play them. Gish builds in general were a lot of fun. There also was a Sand mage in a desert theme manual that was very interesting.
Looks nice. What's it for?