Can't answer that because we don't know you or your likes and dislikes so I suggest that you read up what the different cruise lines offer then read the reviews for the ships you think you might go on and then go ahead and pick a cruise on Azamara Quest or Journey !!!!!!!! .... Sorry research then as us more specific questions. .... Neil.
Neil is very right, but in a nut-shell: RCI are more 'fun', informal and family orientated, Celebrity are a little morse sedate, semi-formal and upmarket. RCI may be a bit cheaper.