Wow. The Apple podcast app looks great but is just utterly horrible on my iPhone 4. Just not stable at all. Some podcasts won't delete, I've had it hard freeze just trying to add a podcast from the store and from trying to play something it had already deleted.
EDIT: I'm about done with Instacast too. Hard to believe it got so laggy/bloaty since I bought it not too long ago, but the lag on loading makes me wonder if they just dev on the 4S. Somebody suggested downcast, right?
Downcast is the best so far IMO. Instacast used to be my favorite. Haven't used the Apple app enough yet, but it looks like it needs some fine tuning.