Don't take my word for it... that was the finding of Forbes magazine.
They've been called passionate and they've been called classless, but if you're selling tickets or merchandise you don't really care. Eagles fans are the most loyal in the NFL, based on attendance variance and ticket sale waiting lists. And devotion keeps the cash registers ringing. They explained their basic methodology. Our final rankings were a combination of a few factors: How closely related fan attendance patterns were to winning percentage. We used what statisticians would note as the P > |t| value and checked for the mathematical confidence of that assessment; as well as the slope of the line as it went from zero wins to 16 possible wins. The sharper the slope broke downward for every point the team lost, and the faster it broke upward for every win, the less loyal fans were deemed to be. Results were controlled for league wide attendance variation. Eagles fans topped the list with the redskins and packers rounding out the top 3. Not surprisingly, Dallas fans did not make the top 10. Could it be because of the disappearing act they do when their team doesn't play well? Could it be because most Dallas fans you meet have never even been to Texas let alone tried to buy season tickets?