Forrest Valkai. He’s a biologist who makes a mixture of educational content, videos debunking creationist claims (in an educational way rather than the “look at this fucking idiot” approach that much of atheist youtube seems to take), and just some silly fun in-between.
He doesn’t have the insanely high production value of other channels named here, but he’s the most wholesome person I’ve ever seen. His love for life and science radiates off of him and watching him passionately explain how cool something is genuinely makes me happy in such a depressing and pessimistic world.