I don't use Good Sam, but I will give you my $0.02 anyway.
First of all, none of these services - AAA, Good Sam, Coachnet, Escapees, FMCA - own their own tow trucks and pay their own drivers. They all try to sign up as many towing companies as they can that will accept their rate. When you call when you are broken down, the operator will start going down a list of towing companies that they work with, trying to find one that's free to head out to your location.
I've seen a lot of threads on this subject, and no matter which company you are talking about, you will find a bunch posts raving about how wonderful they are, and a bunch of posts describing some horror story where the company failed them. Of course, it wasn't the company, it was the towing contractor that was either wonderful or horrible. Luck of the draw.
In some parts of the country, it can hard to find a towing company that can handle RVs. Keep in mind that when a big old motor home of bus conversion is hanging on the end of a towing hook, legally it's the same as a tractor trailer, they need a BIG tow truck, and the driver needs a Class A Commercial License.
If the company is busy dealing with a broken down commercial truck - which pays a heck of a lot better than the RV companies will offer them - then you are So Out of Luck.
I second what darsben said about AAA.
So the best advice I can offer you is to carefully compare the plans offered by Good Sam, Coachnet, Escapees, and FMCA, read the fine print carefully, and pick the one that seems best to you. Be sure to check for such things as whether they will cover you in Canada or Mexico, if your personal plans include such trips.
There you go. Free advice that's guaranteed to be worth every penny you payed for it!