There is really only two hotel booking companies on Trivago, Expedia and Booking.com. The rest are all owned by these two companies, except Trip Adviser but they are partners with Expedia.
Trivago is set up to make it look like there is a lot of competition. But don't be fooled.
I occasionally use Hotels.com which is owned by Expedia. For every 10 hotel nights you buy you'll get a credit for a free night. It's based on the average price you paid for the 10 nights.
If you spent $1000 before tax on the 10 room nights you'll get a $100 credit towards a free night. But you are still on the hook for the taxes. Taxes on hotel rooms can run anywhere from 10% to 25%.
You want to book a room as close to the $100 as you can get. If you book a room for $60 they will take the entire $100 credit for it.
You have to download their app to work the free nights. Collect 10 stamps on the app to get the free room.
You want to be careful when booking two or more consecutive nights. If I book two nights sometimes the app will say I will collect two stamps and other times it will say I will get one stamp. When they try to slick me like that I book two separate reservations.