Blocktrainer should also be mentioned.

https://www.youtube.com/channel/UCG6KtMc5WYB-ppxwpaX5CFw

If it comes to quality I would also add Chris Müller from HelloIOTA, which is not to say that the others are not of good quality (its subjective grading).

https://www.youtube.com/channel/UCfq6x_5wCrXh0mUa-1iRX9g