We are long time RCI cruisers(since the 1970's) and Celebrity ships form day one.
In our opinion the food on Celebrity is significantly better quality and taste. The service is also much more refined. As far as pricing , not much difference.
With the growing size of mega liners on RCI and packing of 3 or 4 thousand passengers aboard we have shifted to smaller ships with fewer passengers and less congestion.
Our favorite class of ship is the Century on Celebrity(70,000 ton range)
RCI has some older ships in this tonnage that also are attractive without holding 5000 people packed on one ship.