As we run two Landrover Discos and do a lot of off-road work and towing, with combined annual mileage of over 50k, then breakdown cover is pretty much an essential requirement for us.
We usually go with the AA because they offer a range of sensible options - we have included the replacement vehicle and also the mechanical repairs sections as well as the bog standard relay cover. This means that if they take your car to a garage to get it fixed they will, subject to approval, pay for the first £500 of any repair. Over the last three years we have claimed on this every year and got more than our premium back.
They do try and ramp up the premiums each year but we just cancel our renewal and take out a fresh cover, alternating the policy holder between myself and my wife.