I've been with the AA for years, so long I get free home-start as a bonus....
Haven't used it very often, had a recovery when a clutch release bearing colapsed, also when my car was written off by a biker. Couple of times I've rung them, then rang back to tell them I've fixed it !
Last time I used it I was in somebody else's car and the head gasket blew (mentioning no names, Pete), they quoted my 1 hour before somebody would be there, but they turned up in 5 mins... and took the car home, almost as quick as driving it home !
I have a cautionary tale, when I was 17 I took out AA cover, didn't use it, and decided "I can fix anything" so didn't renew it. Shortly after I broke down on the M62 with what turned out to be a holed piston, I had to pay to get recovered home, which was £150 (20 years ago), since then I've always been a member, just in case.
Another one to look at is Britania Resue, they've sponsored our local rally a few times so I feel I should support them, however I have no experience of their service.
http://www.britanniarescue.com/