I have tried all of them (Instacast, Downcast, Pocketcasts, Podcaster 5, etc). Downcast to me is a bloated old school 2007 UI and is in need in a refresh. Instacast has a much cleaner UI but I have had a lot of problems with Vemedio's new cloud sync. Pocketcasts doesn't currently support auto downloads so that's out for me. PC is currently being re-designed and if the iOS version looks anything like the new Android version 4 to be released this month then it's going to be killer. Shifty Jelly is a small shop with 3 devs so they decided to Android first and iOS will follow later this year.
After all that being said, I am currently using Apple's podcast App. I have had no issues with podcasts being updated, downloading, and syncing via iCloud. I also enjoy that downloaded podcasts are part of the native DB in iOS that is recognized by my cars' Audio system when connected via USB which means I can browse the podcasts content using the car system. I mostly use BT in the car, but it's nice to have that feature when charging and connected via wire.