Denver. Had a tough schedule and still in contention to win the AFC (Indy, Seattle, Arizona, San Fran, San Diego and Patriots all played).
On the NFC side, Arizona shouldn't suffer through the loss of Palmer too much, as he just isn't much better than the reserve. The Seahawks are still a good side, and San Fran aren't rubbish. Green Bay seem to be pulling themselves together. Think Detroit have just had an easy schedule and strike me as a bit :censored: really (Giants, Jets, Buffalo, Minnesota, Atlanta, Miami), the best team they've played is probably the Saints (who are no great shakes away from their dome) or Carolina who beat them easily. So in short, I suspect the other contender will be Seattle/Arizona.
But Denver.