My favourite is Snake Discovery, she is very positive, sheds a great light on reptiles, and I love how well she cares for her snakes (especially that she puts enrichment in the enclosures even with racks!). Her videos are always fun, interesting, and informative.

I also watch Olympus Reptiles, Josser's Jungle, and TheRoyalConstrictor (I love seeing all the different morphs that are shown in his vids).