The best managers of all time. What a list. Some of the most talented football theorists and motivators alike. Those managers could develop systems that revolutionized football and got the best out of players who before were considered average.
Trophy haul is most certainly an accurate method to measure success. The only possible argument against the measure of success by trophies, is when managers inherit a good squad. Take the example of Avram Grant at Chelsea. He reached two finals ( the FA Cup and the UEFA Champions League) with the squad that Jose Mourinho left. He made no significant additions to the squad. He is not considered as good a manager as may who have done the same.
Also, the value of certain trophies is less when there is not much competition. Celtic and Rangers in the Scottish League is a two-horse race. This allows for managers of either club to rack up titles rapidly without needing to be a quality manager. Same goes for Barcelona and Real Madrid (Domestic Trophies)
Not Selecting Managers who manage a club in a nation which is not in the Top 11 Leagues in the UEFA Coefficient (2007-08)
England, Spain, Germany, Italy, Scotland, Switzerland, Turkey, Portugal, France, Greece and Russia.