I don't often listen to podcasts, but when I do, the most useful ones from a learning standpoint are those in which the host describes everyday things using the first-person so that I learn how to talk like a native speaker. Honestly, the more ordinary, the better.

Bonus points if they are reactions to situations that I can't easily replicate in my home country. For instance--how do Spanish speakers react to films while they're watching them? Do they give commands to the characters ["Hey, don't go in there"]? What are typical expressions ["Not another flashback" or "I really like this background music"]. Small stuff like that is really useful and often overlooked in podcasts that try to be too intellectual.

Also--teach me how to THINK like a native speaker. If you explicitly say, "This is what I would be thinking in my head right now"--that's very useful stuff that is hard to get anywhere else.

Finally, some slang is okay, but I like hosts who are aware enough to refrain from niche expressions that the vast majority of the native-speaking population won't understand. It doesn't seem like a big deal to the native speaker, but it becomes a headache for me, the learner, to do research and realize that it's some really current saying that will be out of style in two years and thus is useless to learn. This is a personal preference though because I'm in it for the long term haha. Good luck with your podcast.