I use Car Rentals all the time, and I am very happy with the service provided. They give good overview of the prices on the market and most of the time allow to find the best deal. Once you are redirected to the provider or another search engine you are on your own. Alhtough most of the time this work fine with me, I had some issues in the past due to realibility of these other search engines i.e. Cafe del Mar and/or the offered by them car hire service providers like easirent.com(avoid no matter the price). You could stick to well known car hire brands, but then carrentals.co.uk does not always have best deals. I recommend the site!