Pittsburgh over Atlanta.
A weak AFC makes me lean towards good, experienced coaching as the difference-maker. That means Tomlin, Belichick, and probably Harbaugh. (I think Kubiak of the Texans, and Fox/Manning of the Broncos aren't good coaches, especially in the playoffs). Since it's hard to repeat, I think the Ravens are out, and I doubt the Patriots have the playmakers on offense to generate points consistently. Meanwhile, the Steelers got a bit younger on defense and have decent depth at RB now.
The NFC is stacked. It could be any number of teams that win this conference (Packers, Redskins, Cowboys, Giants, 49ers, Seahawks,...). I'm picking the Falcons because I think if they stay healthy, they have a pretty easy path to the playoffs and beyond. They play in a relatively easy division (Saints have new defense, and inconsistent offense), they play against AFC East opponents and have the Patriots at home. They play against NFC West opponents, but they have Seattle and St. Louis at home, and they go to San Francisco at the end of the season when they may have clinched homefield advantage). I'm not a huge fan of the coach, especially in the playoffs. But I'll pick the ATL to be different than most of the picks already here. However, I wouldn't be surprised if they get beat in the playoffs again in the second round.
Edit (09/17) - my Steelers pick just looks stellar right now, lol