Comparing Booking.com and Trivago depends on what you aim to achieve, as they serve entirely different functions. Trivago is a metasearch comparison engine designed to scan multiple websites to find where a hotel is cheapest. Booking.com is an online travel agency (OTA) where you actually complete reservations, manage stays, and handle customer service directly. Many travelers use Trivago to search for the best rate and then complete the booking on Booking.com.