I feel like the Seahawks are objectively the #1 team, and it's just a matter of whether you accept that idea or not. They finished #1 in DVOA last season, they had one of the 10 best DVOA seasons since 1991, and they had a shot at breaking the weighted DVOA record going into week 17. Their rise from 2009 to 2012 is one of the largest in NFL history.
Since the end of the 2012 season they've added a pair of top five free agents to their pass rush and traded for a guy that would have likely been the #1 free agent had he been available. Most of their team is young and still trending up. Not only is this the best team in the NFL, people should start asking themselves if this might be a potential dynasty team- the evil team everyone hates because you can't stop them- something like the current Miami Heat team but in the NFL. This team is rapidly approaching an historic classification in terms of talent, IMO.
This is a team that became the first in the Superbowl era to score 150 points over 3 weeks, AND they finished with the #1 scoring defense and a top 3 special teams group. You can attempt to make a case for other teams, but it's not a very convincing one compared to Seattle.