Diaz is awesome. For me, he manages to strike just the right balance between making the topic interesting in a historical/human-interest sense and including enough technical detail to cultivate actual insight. Both his Franck-Hertz and Stern-Gerlach videos are the best I've run across on YouTube (and I see the latter has a part 2 now, so that'll be next on my watchlist.)

Hugely underrated YouTuber.

I also just love his energy. He's unapologetically excited about the stuff that excites him, and even if I don't share all his interest, it makes his videos an absolute joy to watch.