I'm really back and forth with Yuriofwind. He is pretty informative, but at certain times I get really annoyed with his voice, especially when he tries to joke on himself for being socially awkward. He's just not that entertaining and tries to be.
Also, anyone who likes Cr1tikal is a beautiful person.
I don't know enough about gamerrrr cultureeeee to make a list but I really enjoy a lot of the dota 2 personalities.
PyrionFlax is hilarious. SUNSfan and Reaves do a great job with DotaCinema stuff. Purge is an amazingly chill guy and he did a fantastic job casting the rookie stream in TI4.
Aside from Kikoskia (which I rarely watch nowadays), I don't watch Let's Plays that much though I did watch some Let's Plays done by a guy called HHGAMING. What I liked about it was that it was no commentary though one can assume the guy does make these videos for views considering what the description box has. I will be honest and say that I enjoy watching some of PewDiePie's videos. My stance on him is the same as Saney, indifferent to him.
I've watched a lot of different Let's Players, but really only follow a few. And even then, I wouldn't call them the "best". My favorites are Markiplier, psychadelicsnake and StriHiryu.
As for the worst, I'd just be repeating everyone else by mentioning PewDiePie and iJustine.