I'm a big fan of AlphaPhoenix's content. He deserves to be in the big leagues of science YouTubers with SmarterEveryDay, Veritasium, Mark Rober and 3B1B.
Off the top of my head, I remember how the pin failed in the automatic placekicker video, how the cameras worked in the moving dartboard, how they had to use different materials to contain the large scale elephant foam...
Physics Explained is great physics channel that doesn't shy away from math, with derivations of many fundamental equations. His most recent one deriving the Chandrasekhar limit on white dwarf stars from relatively basic physics is great!
The Efficient Engineer is a really good one for clear concise explanations of mechanical engineering principles.