Celebrity Cruises and Princess Cruises both appeal to adult couples and solo travelers — and, to a lesser extent, the family crowd. The big difference: While Princess sticks to tradition, Celebrity tries hard to be current … even cool. Trying to decide which is the right pick for your next vacation? Read on for how they stack up. ItinerariesMost of the Celebrity ships winter in the Caribbean, with a few in South America and Australia. In summer, they spread out, cruising to Europe and Alaska, and only Celebrity Equinox stays in the Caribbean year-round. On the smaller Celebrity Xpedition, which sails to the Galapagos Islands, you get a cushy, soft-adventure experience.   Vs.Princess cruises to the Caribbean and Mexico, and also around the world, offering World Cruises to those looking to check off their bucket lists in one go. The line has a big presence in Alaska and Europe and offers cruises year-round in Australia and Asia. The new Majestic Princess will debut from Shanghai in 2017. ActivitiesCelebrity goes for sophistication, both in its décor — picture cushy sectionals on the main pool deck and hammocks by the glass-enclosed secondary pool — and its activities. Sign up for wine-pairing classes (created with Riedel), cooking competitions (designed in partnership with Bravo TV’s “Top Chef”), and massages in the Canyon Ranch SpaClub. While there is a kids program, very little goes on outside the club to wow little cruisers. Vs.