There are so many hotel booking websites, it's easy to go round in circles.  So I suggest just four. 

1.  Search all the major hotel booking sites at once...

First, try using 'Hotels Combined'. This is a free search tool that checks all the major hotel websites including Expedia, Travelocity, Opodo, Venere & many more, to find the cheapest rates.  Set up in 2005, it's an amazing system, probably the best place to start looking for any hotel worldwide.