I find that the more specialist the guest, the more interesting the conversation, especially when Rogan just shuts his mouth and listens to someone passionate about their field.

Lex Fridman, Brian Cox, and Sean Carroll had--in my opinion--super interesting and engaging episodes.

That being said, there are currently over 1500 episodes, so there are definitely a good number of fluff episodes in the mix as well.

Edit: Just thought of a couple more who I found quite interesting. Paul Stamets and Michael Pollen both discussed in their respective episodes research they both participated in, which made them continuous episodes with a fascinating topic.