Both ships are new, large, and very nice; I might vote in favor of Princess, given you are not into late nightlife and like things a little quieter, but the latter especially will depend on which time of year you are going. There may be more young folks and/or families in school break periods, for example.
Also, food is a very subjective thing. (You will find that out if you read lots of cruise reviews.) I have personally enjoyed meals on both cruise lines, finding the food very good to excellent on each one.