Personally, it's counter strike for me. I bought Counter Strike GO a little while after it came out on xbox. I had heard of some of the fanbase's reputation, but in the end...it truly ruined it for me. The combination of elitism and intolerance towards anything that isn't COD eventually made me quit the game for good.
Don't get me wrong, as with any fanbase, there were exceptions. There were people who were great fun to play with, but they were, sadly far outweighed by the people who really, really weren't.
I suppose that's the thing about online-focused games. If you like a single player game and everyone else hates it, or the fanbase who does like it sucks, it doesn't matter, it won't affect your play in the slightest. With online games, if a low amount of people like it, you won't be able to play at all, and a truly unpleasant fanbase can utterly ruin even the best online games.