It's important to emphasize what is for me the main difference between cruise lines: passenger demographics. I am not being a snob when I state that different cruise lines attract different types of passenger profiles. We can analyze this cruise line by cruise line, but one also needs to look at the length and geographic location of the itinerary. However, overall I think one could accurately state that Regency (or Crystal, Seabourn, etc.) attracts a more upscale, better educated demographic than Celebrity and unless one wants to be secluded in one's suite on Celebrity that is important to keep in mind.