3Blue1Brown is one of the best math educators on YouTube. As a matter of fact, I would say he's the best I know of at the moment. I'm currently working my way through his series on diff-eq.
I can certainly say that no one else has made me tear up.
Not only does he have a penchant for finding geometric analogues for mathematical ideas that are neat and beautiful, his animations clarify and increase my understanding of those concepts.
The "production quality" to use a slightly commercial term, is top-notch.
His python library for generating his visuals is open source and equally as impressive: