Even the cheapest site can, sometimes, be outdone on a one off rate quote. As a general rule of thumb HolidayAutos, because they're a broker, are the cheapest. That said, don't go direct to Holiday Autos website, instead go to www.opodo.co.uk and select car hire. They partner with Holiday Autos and in my experience the quote is always 15 pounds less via opodo than direct viaHoliday Autos website. If you want to book directly with a car rental company www.easycar.com, where available, and www.alamo.co.uk are best (Alamo is almost always cheaper than Hertz).