Which crusade was most successful and why?

To answer this question in the most simplest form you must look at the aim of the crusades; although there were many secondary aims for the crusades the main reason from the first four crusades to embark was to capture Jerusalm, which had been help by the Muslims since 638AD. So taking this into respect the first crusade must have been the most successful because it was the only one out of the first four crusades to capture Jerusalm!