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 Arsenal
There are far bigger rivalries in sport than Red Sox/Yankees, but for the sake of the thread, I'll go with Yankees. Red Sox are only just beginning to even the playing field.