I usually say that Celebrity is better in every category but not by a mile. It's the small things that add up to make a nicer experience. For example the first thing you will get on board is a free glass of champagne.
Celebrity is also geared more to the adult crowd which is good if that's what your seeking. Less crying babies, teens running around, quieter and more peaceful. Also less likely to have a slide/waterpark area, as many people in the club after midnight, etc.