Harriet, I would highly recommend studying the four different "experiences" offered when booking MSC, as each provides different pros/cons. For example, we would not be happy with anytime dining, so we do not book Aurea, but book Bella as that gives us traditional dining. We do not want room service, so do not need Fantastica.
Secondly, if you have a good loyalty status with one of the lines you've sailed, consider doing a status match, which could give you some nice benefits.
We found MSC different from our other lines, but in a good way! I hope you will find the same.