Call of Duty, since I've actually met CoD fanboys in real life, whereas I have never met a TF2 fanboy (or even fan) in person.
And if the fanbase can piss me off on the internet and in person, then it's clearly the worst.
And really, I've never had much of an issue with the TF2 fanbase. Some are a little over-enthusiastic about the game, but that happens in every community.