Windows 10. I was originally okay with another windows version rather than just updates, and then my dad put it on his as an "upgrade" from 7. It was utter shit. Took an old but serviceable pc and turned it into fucking molasses. And that's not even the worst of the bullshit, as it turned out.
So, I grabbed some CDs and burned on some distros and tried shit out. I liked what I found, with the exception of audio.
I'm definitely not obsessed. I don't have brand loyalty, even when the brand is free as in beer. And I'm not evangelical in that I don't inject linux into every fucking computer related conversation. But I do speak up for the fact that we aren't stuck with only windows and no other options, and that I prefer Linux overall.
Now, I am a bit zealous about how much I fucking hate Microsoft and windows, but that's a separate issue imo. But, again, I don't inject that into every conversation.