Christopher Odd, hands down.

Discovered him around the time XCOM2 got released, because I was looking for someone to learn a trick or two from. Learned a lot from how he plays tactical games, but stayed for his calm and down to earth way (I absolutely can't stand that hyper, over-the-top crap that a ton of Let's Players do). Have also discovered the one or other gem through his videos.

Can only recommend!

Oh, and I also watch a ton of stuff on game design due to an interest into game development and recently did a blog post on my favourites there. To quickly summarise that: The Architect of Games, Design Doc, Game Maker's Toolkit, GDC, Noclip, Razbuten