Personally I'm a big fan of Windows 10, which I know will not earn me much love. But it gets the job done, and just feels familiar to me. That said, I've gotten pretty used to OSX in the last 6 years or so, and it's definitely no slouch. Going back and forth between hotkeys on the two OSes is my biggest complaint. That and the poorer OpenGL support on OSX. And the generally underpowered hardware.
Linux is something I have used off and on since the 90s, RedHat 5 or so. For servers I want nothing else; I can't imagine running a windows server these days. As a desktop/laptop OS, I tend to be a bit more wary because of potential driver issues, and program compatibility issues. But Virtual Machines are able to run very hardware-natively on most hardware now, so for cases where you absolutely need a windows install on a linux box, you aren't limited to dual boot.
I got incredibly tired of the dual boot situation years ago, which is what pushed me off linux more. Now I keep a dedicated laptop for linux instead. WINE is also way better these days, and can even run most Arcen titles quite well. I don't know how it will do with GPU Instancing in AI War 2, but all our other titles are DirectX9. Either way, the support for the new Vulkan API is advancing primarily on Linux and Windows at the moment, and in some places faster on Linux (!), so I see a bright future for Linux if that holds true.
The main problem with a lot of linux machines is that they are either something you have to build yourself (and then pray the drivers work or do lots of research in advance), or which are geared towards business users and thus underpowered for gaming. There are a variety of sites that make custom linux rigs that are tested out and built for you, either in laptop or desktop form. I got my most recent linux laptop from System76, who I don't mind plugging because I'm really pleased with their work:
https://system76.com/When it comes to windows, Vista and 8 are both terribad for various reasons. XP is incredibly dated and a big security vulnerability. If you want lots of RAM and such, then 7 or 10 are the ways to go. I didn't think anything would pry 7 away from me, but 10 has. I wish it wasn't riddled with invasions of privacy, but you can turn those off. There's a full-blown keylogger installed by default, which is pretty unforgivable. If linux had as good a feel to me as windows, and the same compatibility, I have zero loyalty to Microsoft.