There's no team I call my second and third favorites, but...
Bears and Packers.
I love football. These two embody football, good football, like no other teams do. Great venues, great history, and great players. Favre was my favorite player in the league when he was a Packer. (Imagine how I felt when he became a Viking!) I really enjoyed watching Reggie White, Brian Urlacher, Ahman Green, LeRoy Butler, KGB, Mike Brown, and all of the Packers' recent receivers. I have also lived in Wisconsin before.
I get that their positives are our negatives, and there is a lot of bad blood between many of the fans, but all that is whatever to me. Not into the Romeo and Juliet type of gang-minded hatred. If the Vikings are in need of a Packers or Bears loss, then I'll root against them fervently, but that's about it.
The Steelers are also a team I loved to watch when they had such great defensive players in the 00's and Ben on O with Ward and Bettis. Sadly they look absolutely nothing like they use to, even if they're still average at worst.