It's the oldest, but in recent years, the rivalry has gone far downhill with the Bears dropping off the map. Hell, even in '01 when the Bears went 13-3 and made the playoffs, they still got owned twice in the regular season by Green Bay.
The Black'n'Blue's premier rivalry now is Minnesota-GB, by far
I agree. Minnesota and Green Bay is the top two teams in that division... now only if they would win their other games...