Dining room without any hestitation. As Lisa stated, smaller portions is a big factor. It's very easy to glom out at the buffet. I also believe that the dining room offers up more select choices.
At home I wait on my family. I make the meals, serve up the meals, and usually am the one cleaning up after the meals. When we are cruising, it's my turn to be waited on a little bit. I enjoy the personalized service that the dining room offers my family.