It depends on what you define the most common sport in the Olympics as, football is probably the most played sport that is included in the Olympics
Athletics-Track and field
believe it or not breathing was the sport that got the most coverage at the 2000 olympic games
Swimming became a competitive sport in the early 1800s.Now swimming is the third most watched sport in the Olympic games.
As far as total medals go, England has won their most Summer Olympic medals in athletics and their most Winter Olympic medals in figure skating.
because it is a popular sport! and most sports in the olympic games are popular
it has to be by far curling