I find it quite interesting the wide range of opinion when it comes to rating cruise lines. Here is a comparison using three major sources. Cruisemate----Cruise Critic---  Berlitz's "Cruising and Cruise /Ships".

Note: Cruisemates and C.C. pretty much base their ratings on the highest percentage members give for cruises using five levels of quality. Berlitz only rates the big 11 and bases their ratings on combined scores of all around service levels and food as judged by a roving team of staffers, as well as some written public input. 

Not exactly perfect comparison criterion but interesting nonetheless.

BERLITZ-----1.  Cunard    2. Celebrity   3. MSC   4. Princess   5.  HAL   6.  P& O    7.  NCL    8. Star Cruises   9.  Costa   10.  Carnival   11. Royal Caribbean    


CRUISEMATE------1. Crystal   2. Disney   3.  Regent and  Silverseas    4.  Azamara and Seabourn    5. Windstar   6. Royal Caribbean and HAL and Celebrity  7.  Oceania and Princess and Cunard   8.  Carnival   9.   Viking   10.  NCL    11.  Costa    12.  MSC         


CRUISE CRITIC------1.  Azamara    2.   Crystal     3.   Disney    4.  Celebrity and  Seabourn    5. Viking   6. Oceania  7. Princess and Royal Caribbean   8.  HAL and Windstar   9.  Carnival  and  NCL and Regent   10.  Cunard    11.  MSC   12. Costa