I have cruised HAL, Princess and Celebrity in the past year. Yes, I am a foodie and have worked in commercial kitchens. I have also worked as a professional taste tester evaluating a wide variety of condiments.
If someone says that all the food on a particular ship is bad, I would find it very difficult to believe. There are so many different kitchens and methods of preparation and the like.
My experience on Celebrity is the the MDR was quite excellent with great service. The menu was acceptable but not remarkable for a premium cruise line. In general, the food was well executed but with several significant flaws (undercooked risotto, raw bananas in Bananas Foster and half cooked chili in their lentils) that should have been caught by the head chef. Our servers anticipated every need. The buffet was generally very good and offered great selections. The burger place was poor with the staff unable to properly cook a french fry.
HAL had the most creative menu in the MDR and found dishes to be nearly flawless. Their international selections on the breakfast menu keeps me coming back. The buffet was good with a more limited selection. I did not like it as much as I prefer to try dabs of 25 dishes and the staff only seemed to want to give full portions. The grill by the pool was very excellent and had some of the best burgers I have had. The New York Pizza was a weak point especially at night. If they ran out of something, you were out of luck. The cafe was also very good when they had the items in stock.
Princess Had the best buffet in terms of quality and great selection. It was confusing at times as to which station was open and when. The food in the MDR was very good and the menu was fairly broad with a good number of the favorites. I was generally impressed with the overall experience.
Personally, I would go back to those three lines on the basis of their food alone.