Coach-net gets first place vote in my book. Then comes the Good Sam/Camping World twins - it's essentially the same service provided by another Affinity subsidiary and labeled either Good Sam or Camping World (also Affinity subsidiaries). Everything else is a distant third, in my opinion.
I add my vote for Coach-Net (as I have several times in the past).
They're the only ERS we've ever had. I have used them--tire blow out and complete loss of the power assist system hence no brakes and no assisted steering in the mountains--and am completely satisfied. One of my best $100USD / year expenditures.
Like a number of others here, I currently have CoachNet. I previously had Good Sam ERS and the only time I needed to use them they were first class. I dropped them a number of years ago because I was unable to get their junk mail stopped.