There's this small Youtube channel called the Yogscast, you probably haven't heard of them. They're a small and unknown channel, with only about five and a half million subscribers.
Seriously though, my vote would have to go to Wooden Potatoes. He has a number of Lets Play series but the reason I subscribed to him is because of his Guild Wars 2 videos and especially his Guild Wars lore. Literally everything I know about the lore of Guild Wars, is because of him. He has also recently started a series called Guild Wars Mysteries, where he looks at aspects of Guild Wars lore that are interesting, but which we know little about (such as the floating wizards castle). If you play Guild Wars 2 but never played the first game, you need to check out his channel.
Epicnamebro is another person who deserves more love. Around 130,000 subscribers, so he isn't exactly unknown but he still doesn't have the attention he deserves. He doesn't make as many videos as he used to, because he's a teacher and just had a child, but his Dark Souls lore series was nothing short of amazing