I have booked hotel rooms using booking.com and tripadvisor.com and found the latter less reliable. I say less reliable because I noticed that they do not publish negative reviews and even if they do publish upon complaint/request from the merchant they promptly remove it without further investigations. I am not sure whether booking.com does the same.

Having checked the best deals on these sites I will then check with independent review sites such as Trustpilot.com and Sitejabber.com and look for negative reviews, if any, of these merchants offering best deals before confirming my bookings.