Personally, after all the experiences written here and elsewhere, I have decided that the solution is to spend an extra $100-$150 and get a second service. At some point, one WILL fail you. With two services, you can get help with the other when the first fails.
I had AAA and GS before. When GS failed, I was able to contact AAA and get the help. Now I have AAA and CoachNet. If one fails, I will contact the other and get help. GS and Coachnet work similarly - they have to find someone to work on your rig before you get a tow. AAA will tow you but you have to tell them where to take you. Between the two types, you'll be pretty much covered in any circumstance. With just one, you'll find times when the one you have doesn't help.