I would say as a 10 year old in 1979 I still rooted for the Packers #1a, but the Chargers were #1b. Once John Jefferson got traded to the Packers in '81, I firmly moved away from the Chargers and cemented my Packers' fandom.
In the late '70s probably the biggest bandwagon team amongst the kids my age was the Dallas Cowboys. I didn't gravitate towards them, but I did root for them when they would play the Steelers dynasty who in their dark black uniforms looked like the representation of evil. I look back now, and those guys from the Steelers were actually really cool guys for the most part.