Louis C.K. Just goes to show how many fantastic interviews Maron has conducted, because I was so sure this one would already be on the list! Actually, it's not so much an "interview" as it is a joint therapy session between two buddies who had a falling out and end up talking over their friendship issues in this very episode. It's very powerful to bear witness to the neuroses of two titans of comedy. Also, Louis talking about the birth of his daughter had me in tears.
PS: When I was looking this up to make sure I had the right episode, I skimmed through a bunch of articles naming this "the best podcast episode of all time." So, make of that what you will!