Difference between dictionary and classified catalogue:

Of the many inner forms of a library catalogue, the most popular ones are the dictionary and classified catalogues. The former has superseded all other forms of alphabetical catalogues like author, title, subject and name catalogues. With elaborate cross references, it has increased its usefulness and capability to meet all the requirements of a library catalogue. On the other hand, the classified catalogue displaying its entries with a panoramic view of the subjects, incorporates many of the features of a dictionary catalogue in its alphabetical index. Therefore, these two forms of catalogues have been adopted by most libraries.  

Both these types of library catalogues should work reasonably well and within limits if worked and operated well. There is no absolute yardstick to measure their merits or demerits.