1982-83 Philadelphia 76ers have the best winning percentage in NBA Playoffs history at .923 (12-1).
The new York Yankees
Yes, they are one of the better NFL teams, though not winning a super bowl, have a .555 franchise winning percentage. 5th highest in the NFL
Winning 8 straight games will do it.
Michigan has the highest winning percentage and the most wins
the colts have the highest winning precentage
The New Zealand rugby team, the All Blacks, have an all-time 74.49% winning percentage.