If Denver gets Romo, they are a serious contender.
Baltimore, should they play NE in the playoffs, is always a threat.
Oakland could be a challenge. Young, talented, with a very good QB that we didn't have to deal with this year.
In the NFC, I think the Giants will be much better than they were, and we know the Giants-Pats playoff history.
Seattle is always excellent.
Green Bay is improved - better health, adding Bennett... they're going to be tough.
Atlanta should be good, but I think they'll tail off.
Fortunately, in the NFC, we don't have to worry about all those teams. Just whichever one emerges from their conference (should NE make it to the Super Bowl).
Honestly, I think the biggest single factor in the Patriots winning it all is...health. If they are healthy, they should win it all. They have the best team. If they aren't healthy, they're deep enough to still be very good, but probably not good enough to win it all.