I started listening to a podcast called Up and Vanished, which is two seasons of 6 episodes. The first season has to do with the disappearance of beauty queen Tara Grinstead. If you've seen Disappeared on the I.D. Network, you're probably familiar with the case. History teacher (and former beauty queen) missing, glove found in yard. It's not bad. The guy hosting the podcast is able to do an amount of investigating that feels startlingly unprofessional for a civilian to be doing (like testing soil for blood).
I finished one, called The Aftermath about a college student murdered in 1979, and found in her apartment. It's produced by a local paper, I believe, in Ohio where the murder took place. The hostess deals a lot with local officials, and an independent group of former investigators called VDOC, I believe. They're famous, and they get pretty mansplain-y with her, in my opinion. But all in all, the podcast is worth a listen.
In the minority, but I love My Favorite Murder. They never fail to entertain me, and I don't mind the quality of the research. They're just armchair murder fans like the rest of us. I feel like I'm among (hilarious) friends, listening to them.
I did some free research for a couple sweet ladies on The Insight Podcast. Ali's from Australia and Charlie's in the States, so you get a good mix of international crimes/missing persons. They're always thoughtful, respectful, researched and they put forth solid theories.
I still listen to Thinking Sideways but they tend to cover weird anomalies now , which I don't really care for. And the older host, (whose name I forget) tends to talk over the two younger hosts, for absolutely no reason.