After three Royal Caribbean cruises, we chose Princess for comparison.
Embarkation was more of a hassle, with a long outside line for 45 minutes (@11am). Once we got inside it was a reasonable 30 minutes to boarding.
Regal is a very nice ship, but layout is choppy and disjointed. Ship is spotless, with constant ongoing cleaning.
Response from TaylorW, Social Team, Princess Cruises
Cabin and balcony were around 20% smaller than comparable Royal Caribbean accommodations.
Very nice day.