I have autonational rescue and they are amazing- (have had about 5 callouts with them including one on a sunday which they drove me the hour back home then came back for me on the monday morning to take my car to the garage).
I have the platinum cover (pick up from home etc etc.) and it is about £66 per year this year for me to renew (despite all my callouts!) so quite reasonable really. I think the first year you are with them you get 15 months for the price of 12.
My only tiny gripe is once we were stranded on dangerous roundabout- did a callout but then a tall dark handsome man came and towed us to safety and temporarily fixed the car for us but said we would still need it towing home- we called them to say the pickup had changed and they got a bit arsey but then they were fine. Phew!
I'm currently with GEM Assist and they've been good, when I've needed them. I've previously been with Green Flag, Britannia Rescue and RAC. The only one of those I wouldn't go back to if the price was right, is the RAC.
Britannia Rescue- can get it independently or through the Civil Service Motoring Association. They use the rescue trucks of independent garages so can get to you incredibly quickly! They even make sure you can get home after leaving your car wherever you want to take it.