I've been in several apps's TestFlight for a couple of weeks. The author of Memmy has so much energy to work on their app, I think it's the most likely to reach production soon. Mlem is a close second, with a closer feel to Apolo, the others (Thunder and Liftoff!) are still alpha quality for now.
I haven't tested Android apps, but I have the impression there are more choices than on iOS. I'd install them all, try them for a week, and pick a winner based on features and development speed.
Development speed is important because there's many missing features in all of them because they're very new.