I used to deliver cars all over the country. The company I worked for had call-out contracts with both the RAC and the AA. In the 2� years I worked in that job, I had over 30 breakdowns. (A lot of the vehicles were finance repossessions and hadn't been serviced for ages). On the majority of occasions, the company called out the AA but they occasionally used the RAC. I never noticed any difference in the service provided.
My own choice, up until recently, has been to use Autonational Rescue. They're one of the cheapest firms but I've never had any problems on the few occasions I've needed to call them. (I've recently switched to Saga, simply because I was offered a good price, with monthly payments when I renewed my car insurance). If you want to consider Autonational Rescue, you can find the details here:
http://www.autonational.co.uk/
Chris
PS: The only minor problem I had with the AA was when they refused to accept that the address I had given them was correct. Their telephone operator stated that I must be wrong; I couldn't be on the car park of Farnum House, Basing View, Basingstoke as there was definitely no such address. I politely pointed out that Farnum House is the headquarters of the AA ;-)