Red Sox never win, so Yankees.
So many great sporting rivalries. Im biased but here is my top 5.
1. "Ashes" cricket, Australia vs England.
2. "State of Origin" Rugby League, New South Wales vs Queensland.
3. Bledisloe Cup Rugby, Australia vs New Zealand
4. England vs Argentina, Soccer.
5. Rangers vs Celtic / Inter vs AC Milan / Man U vs Chelsea
You can't say Red Sox never win when they are 2nd in the division right now, only down 1.5 games, while the Yankees are last and down 5 games.
I agree with you about the Rugby and soccer rivalries. Those are some of the greatest ones in sports.