I pretty much only browse YouTube when I'm really bored or to look for absurd videos with my friends. I like Kim and Hannah of the Yogscast, mostly when they play horror games together. I also like Achievement Hunter's Go and Versus series, but I never really bother with the actual gameplay videos. Actually, most of what I do watch consistently on YouTube is video game content. I'm playing around with running my own channel but I've got too many things going on to give it much effort.
One of my favorite series is Beer and Board Games, which is exactly what it sounds like. Some folks get drunk and play board games, and they are hilarious. My favorite episode is Nightmare III.
As for the kinds of videos I find funny, let me just say this: you can stop at five or six stores, or just one.