I never find there is enough vegetables in the main dining room so I tend to go for the buffet. It took me a few cruises to ever visit the buffet in the evening but I was pleasantly surprised. Good choice with theme evenings and the meats/vegetables change nightly.
I will usually try 3/4 nights specialty dining (14 night cruises) and it is usually a big step up in quality from the main dining room. The only disappointment has been Chops.