Ibf because of some of their policies.
Max 10 pound rehydration limit morning of the fight(Chavez jr or canelp will never fight for the ibf belts).
Also ibf constantly fails to rank a #1 or even a #2, they set up eliminators between top ranked guys in order to earn a title shot. Gary Russell jr would never have fought for the ibf title because he was never willing to fight a top 10 guy.
The WBA is the first belt of the four but its the most unmemorable to look at. The WBA has also left a bad taste with people due to the introduction of super champions and regular champions. That was a horrible idea, someone should have been fired for that.
WBO because they have the nicest looking belts.
WBO
http://www.wboboxing.com/wp-content/uploads/2013/01/WBO-Belt.jpg
WBC
http://www.auctioneers.co.uk/about-us/images/sports-history/boxing/belt-wbc-thmb.jpg
IBF
http://www.countyengraving.co.uk/images/IBF%20Belt.jpg
WBA
http://goldinauctions.com/ItemImages/000006/6836a_lg.jpeg