Neither is 'bigger' than the other as such but overall the PDC is usually considered to be the better organisation if you consider the quality of the players and razmataz of the tournaments. The PDC has more TV coverage which in turn means more prize money available so because of more lucrative sponsorship deals the players are more well paid. Both organisations are allowed to hold their own version of the World Championship of Darts because they both recognise the WDF as the governing body of the sport.