If you’re an empty nester thinking about cruising, one of the biggest questions I hear is: Which cruise line fits our travel style now? Two of the most popular options I recommend are Royal Caribbean and Princess Cruises—and while both are excellent, the onboard vibe is very different. Knowing where your cruise dollars (and time) are best spent can make all the difference.

I hear two big misconceptions about cruising all the time. Either people think it is completely all-inclusive, or they assume you have to pay for absolutely everything once you get on board. The truth sits somewhere in the middle, and it also depends heavily on which cruise line you choose.

Royal Caribbean’s newest ship, Icon of the Seas, is setting sail for its first voyage, and it promises to be more than a cruise—it’s an...