With a dizzying number of websites vying for your travel dollar, it's helpful to remember that there are really just two big conglomerates. Booking Holdings is the largest, as the owner of Booking.com, Priceline.com, Kayak.com and others. Expedia Group follows with brands including Hotels.com, Travelocity, Orbitz, Hotwire, HomeAway, Trivago and many more.

Together, this duopoly of online travel agencies (OTAs) controls most of the hotel booking market. But the consolidation has led to less competition and fewer killer deals, because most sites draw on the same inventory and prices.

What's a hotel-seeker to do? Your best bet may be to scour the travel site of your choice — good old Google also works well for this — and then book directly with the hotel. Hotels have recently struck back at the OTAs, often offering lower rates than can be found elsewhere. Better deals may be in the form of bonus amenities, loyalty points or superior flexibility and refund rules. And when you book directly, you might get better treatment — a room with a view, for instance, or less buck-passing when something goes wrong.

Still, the OTAs may work for you. Expedia.com's size makes its rewards program useful. Hotels.com has a simple "collect 10 nights, get one free" plan. Booking.com prefers instant 10-percent "genius" discounts on select properties for those with an account; the site also competes with Airbnb by sprinkling in choice vacation rentals. TripAdvisor is beloved for its trove of customer reviews, photos and advice.

Innovators include the mobile app Hopper, which has added hotel price forecasting (currently for iOS only) to its airfare tools. The startup Waylo claims to predict the best future price for your room and then guarantees that rate for you. After you reserve a refundable room on any site, Pruvo looks for better rates and helps you rebook. Splitty attempts to "hack" your reservation by splitting it into multiple bookings, producing savings. And for last-minute travelers, the Hotel­Tonight app unloads unsold rooms for same-day check-in, often at a discount.

Simon Peter Groebner