I would go on Princess. It is one the nicest cruise lines, with pretty ship's, great food, and great guest services! We LOVE Princess a long with Disney, though I really would also like to try Celebrity. I have heard great things about them!
We have cruised with RCCL and hated it. We then tried Princess and LOVE it. To me, Princess service is the closest thing to Disney service you will find at sea. The crew is great and polite, helpful and fun. The ship's are immaculate, and beautiful. The buffet is the best, bar none. Horizon's Buffet is amazing on the Royal and Regal Princess ships.
But we always do at least one
Disney Cruise a year, though we do multiple weeks, back to back to backs on the Fantasy!..AND we now do both cruise lines each year, Disney in Spring, and Princess in the Fall. We really love both Disney and Pincess cruises. Itinerary is why we do both each year, different islands or areas of the world!
It all depends on what you want to do on the cruise and what is important, entertainment, casinos, family activity, or the itinerary. It also depends on age group. Holland is all senior citizens or so I have been told, Princess is a mixture, but very few children, Disney is family oriented with lots if kiddos. We have not done Carnival, but many cruisers I have spoken with on cruises tell me they are true party ships! I do not know much about Norwegian, or cruise lines from Europe. I have heard Celebrity is great! I have also heard wonderful things about some of the cruise lines with the large yacht type ships, but they ae very expensive!
It really depends on what you want on a ship and also very important, the itinerary! The itinerary is why we have chosen to do Princess cruises along with our annual Disney Cruise. They go to places Disney does not! It really is as simple as that and word of mouth from fellow cruisers who describe their experience on particular lines.