Several of mine have been mentioned, chiefly the Superbestfriends, so I won't elaborate on them. I do find it curious that I've been a very Internet person for ages, and despite being around for their heyday, I somehow managed to avoid being aware of things like AVGN and all those related, Jim Sterling, Ray William Johnson, Iddubs, all of those. I only found about them as they began falling from grace. Also GameGrumps, although that one was kind of intentional; I knew Arin in a forum before he was famous, he was an asshole (tho so was I) and we'd constantly be in the opposite sides of flamewars over dumb teen forum shit, and when he started getting famous for various things, I always avoided the things.
Also, anyone who troons out loses me. Not for the trooning itself, but it comes bundled with so much mental illness and bullshit. I mean just look at Digibro and the PCP, how quickly the cancer spread in that group, and how brutal the various backstabbings were.
Anyway.
It wasn't watching, but following his works: Andrew Hussie. Seeing how success and tumblr audiences absolutely ruined him was quite eye opening.
A more recent one, the Midnight's Edge people. They were so good at media analysis, responsibly reporting on leaks and rumors, etc.
Now all they do is hours upon hours of boring streams with has-been "industry insiders", bitching about Disney, presenting deranged fanfics as "industry analysis", and then coping and coping and coping when their claims don't pan out.
And they're not even wrong about the things they complain of, yes Disney and Hollywood are rotten with SJWs, but do we need 3 hours every fucking day saying the same shit over and over?
They'd moved those streams to a secondary channel, to keep the main channel for their much better editorials and reports; NO ONE WATCHED THE SECONDARY CHANNEL, so they started putting (boring) clips of the streams on the main, and eventually brought the streams back to it. Now it's most of what they do.
It fucking sucks.
Still, it was fun to see how quickly they dropped and damnatio memoriae'd MundaneMatt after the Boulder incident.