WHEN & HOW I USE THEM:
WHICHBUDGET.COM is the place that I go to first. When you search for flights, in the right hand column, it tells you who are doing the best deals (on any date). This tells me which airlines to look at first.
They consistently find the cheapest deals… deals that other sites (that, behind the scenes, may be affiliated to specific airlines) do not display.
ALSO WORTH A LOOK: