Hm, I guess I would have to say:
I watch videos by PokeCinema [http://www.youtube.com/PokeCinema] the most probably. As his name implies, all of his videos pretty much are based around pokemon.
I usually watch BlameTruth [http://www.youtube.com/user/BlameTruth]'s videos almost as much as I watch PokeCinema's. This guy primarily does CoD and Pokemon. I don't really care for the CoD but I like his commentaries.
GonzoSSM [http://www.youtube.com/user/Gonzossm] has some awesome, yet insane animations. If you wanna see a minecraft man rape a creeper, or see Goku kamehameha that one bald saiyan from DBZ who was with Vegeta up his bum and through his mouth, then this is the channel to watch.
Cry Plays [http://www.youtube.com/user/ChaoticMonki] I just found this guy fairly recently. Another LP'er and he does some pretty funny lps. He is in the middle of playing a Japanese dating sim about birds. Namely pidgeons.
ScottFalco [http://www.youtube.com/user/ScottFalco] Another animator. Has some cool/funny animations, but much more tame than GonzoSSM. This guy did an animation for that Super Mario Hyadain Western Show or whatever that was called by the way just in case you have ever seen that video.
Yet another LP'er, I just started watching PewDiePie [http://www.youtube.com/user/PewDiePie] a little while ago. I'm not going to lie, the main reason I started watching his videos was because a lot of my friends watch his videos. I did, however, enjoy his playthroughs of IB and McPixel quite a bit though, but I haven't really seen enough of his videos to determine whether or not I really like him or not yet.