Besides the obvious, of course.
Number of passengers
Ocean: Up to 6,296 (Royal Caribbean’s Oasis of the Seas).
River: Up to 190 (on Viking River Cruises).
Ocean: Remote islands like Tahiti, major Mediterranean ports, far reaches of the globe (the North Pole region, for example).
River: Inland cities and towns most oceangoing ships can’t get close to (like Luxor, Egypt, and Budapest).
Ocean: From ATV jungle treks to Zodiac boat trips to ice floes in Antarctica.
River: Small-scale walking tours with individual headsets that allow everyone to hear the local guides.
Ocean: Many dining rooms, many seatings, many menus. Wine costs extra on all but luxury lines.
River: One dining room and one seating, with daily multicourse menus. Wine is included.
Ocean: Large-scale, highoctane events, like Broadway shows and club nights.
River: Low-glitz cultural happenings, such as folk dances and craft demos.
Ocean: Water parks, cigar bars, ice rinks, 4-D cinemas—even a skydive simulator (thank you, Royal Caribbean).
River: Libraries, sundecks, small fitness centers, 24-hour coffee bars, free Wi-Fi. And not a kids’ play area in sight.
What it costs (per person, per day, double)
Ocean: As low as $100, though you’ll pay extra for everything but onboard dining and entertainment.
River: From $250, but usually higher. Wi-Fi, meals, alcohol, and most excursions are generally included.