In recent years, reports of health scares and mechanical malfunctions have raised questions about cruise safety. As a result, many travelers are wary of whether a cruise is the best vacation choice.But here's the reality: With a growing demand for improved safety measures, immersive itineraries and innovative onboard entertainment, cruise lines attract an increasing number of passengers each year — and for good reason. In January, the Cruise Lines International Association estimated 21.7 million travelers would take a cruise in 2014, up from 15 million in 2010.With the introduction of new ships, high-tech amenities and extended time in port, the industry is striving to lure millennial, multigenerational and first-time cruisers of all budgets and ages. And when you consider that all meals, activities and lodging are bundled into one rate, it's easy to see why cruise vacations are steadily growing in popularity.But once you've decided to take a cruise, comparing ships and itineraries can be exhausting. That's why U.S. News compiles the Best Cruises rankings. Our annual lists include 15 major cruise lines, ranked based on their reputations among travel experts, guest ratings from Cruiseline.com and health inspection scores collected from the Centers for Disease Control and Prevention. After evaluating the data for each cruise line, we've identified the lines that offer the best experience in the following categories.In Pictures: The Best Cruise Lines of 2015For the second consecutive year, Crystal Cruises earned the top spot on our 2015 Best Luxury Cruise Lines list. Thanks to multimillion-dollar renovations in 2013 and 2014, Crystal Serenity and Crystal Symphony now offer even more standout amenities, including an herb garden (on Serenity) and an outdoor Fitness Garden (on Symphony). Apart from its ship upgrades, Crystal Cruises outshines competitors with its exemplary service, gourmet dining options and unique enrichment programs, such as tai chi lessons and food and wine tastings. What's more, Crystal Cruises received a 4.6 out of 5 traveler rating — the highest of all 15 cruise lines. Small luxury line Silversea Cruises reclaimed the No. 2 spot due to a combination of personalized service (the line maintains a nearly 1-to-1 crew-to-guest ratio), all-suite accommodations and a 4.2 approval rating among travelers. Regent Seven Seas Cruises also kept its No. 3 title, thanks to its luxury cabins, complimentary shore excursions and unique culinary offerings. Finding a budget-friendly cruise is one thing; selecting an affordable cruise that doesn't compromise quality is another task altogether. Best Cruise Lines for the Money ranks the cruise lines that maximize comfort and convenience without leaving a major dent in your wallet. Royal Caribbean, with its ice skating rinks, zip lines and surf simulators, reclaimed the No. 1 spot this year. Apart from the line's versatile amenities and low rates for 2015 itineraries, Royal Caribbean reigned supreme thanks to its well-balanced combination of high traveler, expert and health ratings. Those in search of great value along with even more family-focused cabin options and kid-oriented amenities should consider Disney Cruise Line, the No. 2 cruise line for the money and the No. 1 cruise line for families.See: Is a Cruise for You? 7 questions to ask before you commitFor many families, the perfect cruise provides kid-friendly services and cabins spacious enough for the entire group. But once you've narrowed down that list, picking the cruise that will satisfy all members of your crew can be tricky. Disney Cruise Line, the No. 1 cruise line for families, appeals to a wide range of age groups. On a Disney cruise, younger guests can enjoy character meet and greets and sign up for educational programs in the ship's animator's studio. Meanwhile, travelers ages 14 to 17 can hang out at the exclusive teens-only lounge. And grown-ups can take advantage of adults-only restaurants, nightclubs and lounges. Like Disney, Royal Caribbean caters to a variety of interests thanks to its poolside film screenings for kids, video arcades for teens and fitness classes, spa treatments and wine tastings for adults. Plus, Royal Caribbean's 3.9 approval rating among families helped it take the No. 2 slot for the second consecutive year. Larger groups seeking spacious cabin options and a variety of shore activities should also consider the No. 3 cruise line on this list, Celebrity Cruises. Celebrity offers "Family Tour Challenge" excursions, which range from learning to pilot a gondola in Venice to flamenco dancing in Barcelona. When searching for the perfect cruise with your better half, you want to consider criteria like couple-friendly services, accommodations and atmosphere. But you also want to factor in the opinion of like-minded travelers. Thanks to a 4.7 approval rating among couples, Silversea seized the No. 1 place on our Best Cruise Lines for Romance list this year, edging out luxury competitors Crystal Cruises, Cunard Line and Azamara Club Cruises. Aside from its high approval rating among couples, Silversea offers customizable shore excursions along with activities designed with duos in mind, such as wine tastings, cooking lessons and dance classes. And if you are celebrating a special occasion, such as a honeymoon or anniversary, Silversea provides a variety of memorable cabin add-ons, such as Champagne, chocolate and flowers. Crystal Cruises and Azamara Club Cruises, which took the No. 2 and No. 3 slots, respectively, also provide a myriad of specialized packages. Crystal touts flower and photography services, along with wedding and vow renewal ceremonies, while Azamara features "Bon Voyage" gifts that can span anything from Champagne to spa vouchers.See: 9 Things You Should Know Before Booking Your Next CruiseWith more than a third of all cruise ship itineraries covering the Caribbean, chances are you're considering a cruise to ports of call in this part of the world. For the second year in a row, Disney Cruise Line captured the No. 1 spot on our Best Cruise Lines in the Caribbean list. Though Royal Caribbean and Carnival offer a greater number of scheduled Caribbean itineraries in 2015 and 2016, Disney Cruise Line held on to its title thanks to its superlative Overall Rating and its high percentage of Caribbean bound-itineraries. Disney's four ships offer a variety of shore excursions, ranging from rainforest treks in St. Maarten to snorkeling and kayaking adventures in St. Kitts. Disney also owns Castaway Cay — a private Bahamian island that's only accessible to Disney passengers, where guests can take advantage of child-friendly and adults-only activities, including meet and greets, yoga classes and seaside massages. That said, if you decide to sail to the Caribbean with Royal Caribbean or Carnival, which earned the No. 2 and No. 3 spots this year, respectively, you'll be rewarded with ample shore excursion offerings. Royal Caribbean boasts unique tours, such as eco-safaris in Grand Turk and off-roading adventures in Bonaire, while Carnival features ziplining expeditions in St. Lucia and horseback riding in St. Maarten, among other adventures. See: U.S. News Best Cruises RankingsAbout the author: Liz Weiss is an editor for the Travel section at U.S. News. You can follow her on Twitter, connect with her on LinkedIn, circle her on Google+ or email her at firstname.lastname@example.org.