Economics is a function of social behavior. Specifically about the choices that people make. It fact it is argued in academic circles as to the results of this science .
The least favorite are usually the teams in smaller metropolitan markets. That is due to the fact that they cannot compete with the larger teams financially. As a result, they don’t have the funding to pay the top players in free agency that huge stadium deals provide to larger cities. That is an economical aspect of the NFL.

However, the NFL’s recent “parity” and “revenue sharing” have been much more successful providing competitive games. This result has somewhat leveled the playing field as to a “bottom tier” popularity contest. The rivalries and history within the league, coupled with the rising overall revenues, would suggest least popular would be a function overall team revenue.

Every NFL city will have its local fan support, the overall way to economically measure popularity is quantitatively as stated by economic impact a team a team produces.