I don't know if lines from SFM works count, but I think the "Does it say you want the bucket?" Is my favourite. I like using it to completely invalidate any opinion about TF2 being serious.
https://medal.tv/games/tf2/clips/grAo4a3yzfrBp/9TOjOjGbWNSJ?invite=cr-MSxVNTksMjI4ODY0MzAs
I like this one a lot, dunno if It's good enough material to go up against you lot's clips with.
Probably gonna have to say Castle Crashers, since I got TF2 for free, meaning there was no money to be 100% worth the expense. Got my gray knight to the 90s in levels and can wreck pretty much anything XD