It wouldn't take a lot for me to switch away from Apple's Podcasts app. It crashes all the time, it's impossible for tell why it randomly doesn't play, I'm never quite sure I'm getting all the episodes of podcasts I subscribe to, syncing is pretty bad across devices. The list goes on.
Luckily, Overcast goes well above and beyond. The app is very well designed, the player is fantastic, and the browsing interface is the best I've seen. I'd also be willing to bet that the server-side is rock solid, so your subscriptions will be well taken care of.
If you're a podcast fan, get it. And pay the $4.99 to get all the features - totally worth it. I don't really care about the smart speed feature but the voice boost is really nice to have in the car (which is primarily where I listen to podcasts).