Dan Carlin's format hit it out of the park for me. Just him, in a clear speaking voice, researched and fully edited. I hate co-host banter especially when I just want to hear about the topic, and even more so if they're trying too hard to be funny or they have grating voices.

So to that end, here are a few podcasts I listen/have listened to;

Dan Carlin's Hardcore History

Song Exploder

SCP Foundation Database

Jocko Podcast (*sometimes)