Connaught Bar, Connaught Hotel, Mayfair, London
There are many lists: “Best Bar in the World”, “Best Bars in America”, “Best Bars in This or That City” and following are links to a few of the best of these lists.
http://www.esquire.com/bestbars/complete-list/
http://www.foodandwine.com/articles/where-to-go-next-best-bars-in-the-world
http://www.worlds-luxury-guide.com/Food-Beverage/Bars-Clubs/Best-Bars-World/Best-Bars-World