For Android: It depends on your needs. For better user experience I’d say PocketCasts. For best customization Podcast Republic, Podcast Addict. AntennaPod was for a while the only open source project, PocketCasts is now open source too. If that matters to you, go with those. I like AntennaPod, specifically the sleep timer. However it has some downsides: discovery / search sucks and it’s hard to access the queue quickly if your phone uses gesture navigation.

For iOS: pocket casts, overcast