Marco Arment wrote his own audio engine using Core Audio for Overcast, which enables him to include a lot of clever features. Overcast has "Smart Speed," which will save you time by shortening the silences in talk shows without it sounding artificial. A "Voice Boost" feature normalizes and boosts the volume so everyone in the podcast will sound loud and clear. You can also create smart playlists with show priorities, filters, and sorting rules.
The limited version of Overcast is free, but you can unlock all of the features for $4.99. Overcast is still a new app, so there are things that even the unlocked version doesn't support. It currenty only works with audio podcasts, and it doesn't support podcast streaming -- shows must be downloaded first.
To hear about Overcast and the other Mac and iOS picks this week, check out MacBreak Weekly episode 412.