Besides the All Blacks are the best team in history of rugby and one of the most dominant nations at any sport, I can't assure they have the best winning percentage.
Trying to find winning percentages over 60%, we have:
Kentucky State in College Basketball: 75.8% (only one higher)
All Blacks in rugby: 74%
Alabama University in College American Football 73.5%
San Antonio Spurs in NBA: 61.4%
P.D: Supremacy is not only said by statistics. To take an example, Argentina at polo:
A polo player is graded with a handicap betweeen -2 and 10 to rate its game value. At world polo cups, handicap of a team is limited to 14 to make a spare match .
However, Argentina could join a team handicap of 40 with no big effort. In local tournaments It's uncommon to find a team with a hanicap lower than 30.
As it is: it's impossible to concieve the real potential of the team, but It is so accepted that they're the best they have no need in playing. To me, this is the most notorious supremacy in ANY sport. Ever
----- Below is the answer from NZCoyote-----
In my true sporting opinion, the greatest ever sports team in ANY sport would have to be the New Zealand All Blacks, rugby's most successful team ever.
In over a hundred years of rugby, the All Blacks hold an 84% winning record against all oppostion played. They have also won 74% of all test matches played, and hold a winning record against EVERY TEST NATION IN THE WORLD (including the British & Irish Lions, and the World XV).
Romania (the best team in Eastern Europe), Canada (the best team in North America), Japan (the best in Asia), and other World Rugby Heavyweights Ireland, Scotland, Italy, Argentina, Samoa, and Fiji have never beaten New Zealand.
The average margin when playing the All Blacks is 25-12- that is, they have scored more than twice the amount of points than all opposition combined.
New Zealand is so good, that they have never been ranked lower than 3rd on the World Rankings. In 1987, they were crowned the first ever Rugby World Champions beating France in the final 29-9.
Since 1996, when rugby became professional, the All Blacks have played 149 games, winning 121. Their victories have lead to 9 Tri-Nations Championships in 13 years, play-off appearances in every World Cup to date, a first ever test series victory in South Africa, 7 undefeated tours to Europe; including 2 Grand Slams Tours(when a team plays England, Scotland, Ireland, and Wales in succesive weeks and win), a test series whitewash against the British & Irish Lions, a World record 30 test victories in a row on home soil (spanning five years), the Bledisloe Cup, and the Hillary Shield.
Only five test nations IN HISTORY have ever beaten the All Blacks- Australia, South Africa, France, England, and Wales (who have not beaten New Zealand since 1954). The most successful team to ever play New Zealand is South Africa (winning just 40% of the time), while Australia have won the most times (39 victories from 132 matches).
This small, tiny nation boasts a player pool of just 90,000- yet they provide the bulk of the Rugby Hall of Fame.
Not even the great Brazilian Football Team can match the proud winning record of New Zealand. The same applies to Canada in Ice Hockey, Australia in Cricket, or any professional sports team from the United States.
The All Blacks. LEGENDS.
The New Zealand rugby team, the All Blacks, have an all-time 74.49% winning percentage.
That would depend on what team has the best winning percentage in the league. Generally, the wild card team plays the division winner with the best winning percentage. However, if the division winner with the best winning percentage is in the same division as the wild card team, then the wild card team will play the division winner with the second best winning percentage and the division winner with the best winning percentage will play the other division winner. MLB is the only major sport that sets up their playoff system this way. This would keep the Yankees and Red Sox from playing in the first round of the playoffs.
Through the 2008 season, the Tampa Bay Rays have the worst lifetime winning percentage of any MLB team with .417 (742-1037).
The St. Louis Cardinals.
New york yankees
As of the 2013 season, the college football team that has the best winning percentage in Division 1 is Old Dominion with a winning percentage of .767. Old Dominion has only played 60 games in Division 1 though. Notre Dame is 2nd with a percentage of .733 Michigan is 3rd with a percentage of .732
The 1906 Chicago Cubs have the best winning percentage for a season with .763. The Cubs 1906 record was 116-36.
The New England Patriots have the best win percent since 2011, with a 3 season average winning percentage of .771.
As of 2013, the baseball team with the worst winning percentage since 2000 is the Baltimore Orioles, with a 0.431 winning percentage.
Through the 2010 season, it's the Chicago Bears. They have a record of 704-512-42 for a winning percentage of .579.
jacksonville jaguars are .700
New York Giants!!!
Tampa bay rays
1982-83 Philadelphia 76ers have the best winning percentage in NBA Playoffs history at .923 (12-1).
Teams with at least 4 World Series appearances, the Pittsburgh Pirates have the best winning percentage. 5 World Series titles in 7 Appearances, 5 -2 for a .714 winning percentage. Teams with at least 10 World Series appearances, the New York Yankees have the best winning percentage. 27 World Series titles in 40 Appearances, 27 -13 for a .675 winning percentage.
Through the 2007 season, the American League team with the most wins in a regular season was the 2001 Seattle Mariners with 116. The American League team with the best winning percentage in a regular season is the 1954 Cleveland Indians who went 111-43 for a winning percentage of .721. Seattle's record in 2001 was 116-46 for a winning percentage of .716.
New York Yankees.
The University of Michigan.