We did our honeymoon on NCL back in '79. Our 5th anniversary was also on NCL. Our 10th, 15th and 20th were on Royal. Our 25th was on Princess. We also did two family cruises, one on RCI Explorer and one on the Carnival Glory. We leave on the 15th on the Carnival Triumph for a quasi family trip.
Of all the cruises, the best were our 15th and 20th both on the RCI Majesty. It had the best food and service and were the most romantic. The Princess was a close third. IMO the smaller ships have better food and service.
I am not saying the other cruises were bad, they were all great. For families, the mega ships are best. For anniversaries the smaller ships IMO are better.
After all is said I guess if you had a bad experience on RCI I would recommend Princess since I have no experience on Celebrity.