If youre talking league titles Liverpool has won the most titles in England(Boo), either Rangers(Scotland) or Linfield(N.Ireland) has won the most in the UK and I think Real Madrid has won the most European Titles. Dont know the most in the world.
League titles aside and using cup and european competition also which would be a greater indicator of higher level success then it would be Liverpool (still though some might argue for Man U), Celtic, Linfield and (of the high strength leagues) Real Madrid....World title might see Santos of Brazil but most likely Real Madrid for that also.