Depending on the era:
Being the best team in NBA for sometime it varied between:
Detroit Pistons (Hacking MJ; The Detroit Bad Boys Champions 1989/1990, Bulls 1991-93)
New York Knicks (Eastern Conference Championship Rivalry Ewing Vs MJ)
Indiana Pacers (Jordan Vs Miller; the infamous fight)
Utah Jazz (Stockton and Malone Vs MJ and Pippen; who is the best dynamic duo of baskeball)
In my opinion, I'd say Detroit due to the fact that their was hatred their, a violent rivalry and you will notice the NBA still do talk up Pistons Vs Bulls matches as something big as traditionally these teams have been solid in the East but not too recently have Chicago.
The New York Yankees and The Boston Red Sox.
Before they moved to Washington, the Montreal Expos were also a rival of the Blue Jays.
The rays are another division rival
Toronto Blue Jays was created in 1977.
The Toronto Blue Jays started as an expansion team in 1977 along with the seattle mariners.
Toronto Blue Jays (in Canada).
Toronto blue jays
Jose Reyes is number 7 on the Toronto Blue Jays.
Melky Cabrera is number 53 on the Toronto Blue Jays.
Bobby Korecky is number 51 on the Toronto Blue Jays.
Brad Glenn is number 55 on the Toronto Blue Jays.
Brandon Morrow is number 23 on the Toronto Blue Jays.
Brett Cecil is number 27 on the Toronto Blue Jays.
Brett Lawrie is number 13 on the Toronto Blue Jays.
Darin Mastroianni is number 33 on the Toronto Blue Jays.