The most popular is Fantasy Football (by far), followed by Fantasy Baseball. There is also Fantasy Hockey, Fantasy Basketball and Fantasy NASCAR which all seem to have about the same following.
The least popular sport is volleyball i checked 100 sites no lie x
The least popular Olympic sport is football.
Fantasy Football: I think that's why it's so popular. With only one game per week, players have plenty of time to digest information and make roster changes.
Yes, it's far and away the most popular fantasy sport and contest. Probably to due with it's ease and the fact that football is the most popular American sport, all games are on tv, etc... I know at The Fantasy Jungle, it is far and away the most popular contest that they have. (http://www.fantasyjungle.com) They have a pay contest with a $50,000 grand prize as well as a free game with over $10,000 in cash to the winners. Some of the other popular fantasy football games are ESPN, CBS, and Yahoo.
marbles, which is actually a sport
basketball.
Generalizing would be wrong. Every country has a popular sport and an uncommon (even obscure) sport.
Seal clubbing.
probaly cricket
probably basketball
Bowling
curling