I'd say VSauce(all of their channels) for their interesting videos, Phyrnna for their music, MetalFortress for his Pokemon and Terraria covers, NCHProductions for his animations, and Fabuchs for his funny, well edited gameplay videos.
As far as LPers go, I'd say ProtonJonSA is easily my favourite.
ProtonJon's videos and livestreams are amazing. His streams can summed up with 3 words: "madness", "glitches" and "eggs". ProtonJon is the reason I know about such wonders as Pepsiman, Hatriss, and the Knytt Stories custom adventure thing: "Don't Eat the Mushroom".
Too bad he often goes long periods of time without uploading anything, either because of everything breaking on him or real life getting in the way. Usually both. For example, his Superman 64 LP was started in 2010 and because of the recordings breaking on him, it keeps getting delayed. He has yet to have gone past Stage 7 because of this.
I also watch the other Runaway Guys(ChuggaaConroy and NintendoCapriSun) and TomFawkes. I occasionally watch the Game Grumps one-off episodes, and if they're doing a series with a weird/interesting game, I'll watch it.