Ocean: All but the smallest of these ships are loaded with onboard extras, such as large gyms with classes, swimming pools, a movie theater, and family and kids programs for all ages. You can treat yourself to a massage or facial at the spa before heading to one of the specialty restaurants for dinner. You also have a wide choice of cabin styles, from small interior spaces with no view of the ocean to large balcony suites.

River: A river ship might not have a pool, spa, or fitness center. And if you do get any of these, they will be small, meaning there may be a small plunge pool on the sundeck, or a cabin with a massage table that counts as a spa. Public spaces are limited, with just a main dining room and one lounge or bar area where you also will gather for entertainment — the kind that tends to focus on cultural enrichment.

Ocean: Mainstream ocean cruise ships hold from around 2,000 to more than 5,000 passengers. They are designed so that you don’t feel too jam-packed, but space gets tight at the buffet and around the pool on sea days. Herding all of those people on and off the ship while in port is also quite a feat.

River: River ships typically hold about 140 to 190 passengers spread over a simple four-deck layout. Meals are open seating in one main dining area, and you will get to know almost everyone on your ship. It's an intimate experience, and much more low-key, but it's also a lot of togetherness.

Ocean: If you want to be active and try new things, ocean cruise ships keep upping their games with fun and challenging activities, including rock climbing walls, zip-lining, and ropes courses, not to mention ice-skating rinks and surfing simulators. In port, these ships also provide a vast range of excursions to choose from, such as diving and snorkeling trips or dogsledding adventures.

River: If you fancy yourself a history and culture buff, this is the choice for you. River cruise ships tie up right alongside city centers in historic destinations along rivers such the Rhine or Danube, where walking tours provide a rich history of the architecture as well as time for mingling with residents and sampling the local cuisine — including wine and beer — in quaint village squares.

Ocean: Dinner is just the start of the evening on ocean-going ships. From wine to craft cocktails to beer, you can find whatever you want to wet your whistle at the numerous bars and lounges. You'll also find dancing, karaoke, live music, trivia contests, and talent shows in these venues. Or head to one of the theaters to get wrapped up in a Broadway-style musical or shows with acrobats or magicians.

River: The crowd is older (think 60s and up) on a river cruise. The rhythm of the day sees the ship quieting down not too long after dinner. Most head back to their cabins to rest up for the following day. You may find a few people at the bar for a digestif, but no one is burning the midnight oil.

Ocean: Major ocean cruises can start at around $100 per person per day, which includes meals, entertainment, and lodging. From there, you can add on extras as your budget allows. So it's up to you how much you spend on alcohol, spa treatments, shore excursions, and specialty dining.

River: These cruises are ostensibly all-inclusive. Most lines include a daily excursion in your fare, which is typically a basic walking tour around a historic town. In addition, lunches and dinners often come with beer and wines, and Wi-Fi is increasingly becoming complimentary. Some also roll airfare, transfers, and pre- and post-cruise hotel stays.