What 40k YouTube channels do you recommend?

For Hobby History, I recommend Arbitor Ian. He's an old grognard like me who has been collecting for decades, and explains some of the interesting changes and old lore of the setting (stuff from as far back as when Space Marines all had "born to kill" type graffiti all over their armour). He also does a "Tale of four gamers" type thing with some other hobbyists, and it feels a bit like those old White Dwarf articles come to life. Lots of nostalgia, but also new lore too.