Not sure about favourite, but:
Clint’s Reptiles (zoology, not just reptiles) is nice! Not sure how I feel about the reaction content, but he does stuff like animals-as-pets reviews, animal phylogeny videos (evolutionary trees) and some other videos that might be more interesting/understandable to watch.
Cleo Abram (various science and tech stuff) is fun, though I mostly see/watch the shorts. Similar with NileRed (chemistry), but his videos can be pretty long, haha
There’s also an official animated series of xkcd’s “What If?”! The videos aren’t long, but they’re fun.
Started working on some extra stuff for a miniature environment thingy yesterday, so that was fun. Also pretty recently finished a little hognose snake (by ComplicatedKnots - YouTube)!