We were given Coach-net with our first coach purchase 13 years ago and have kept it in force ever since through three coaches. The first coach was towed twice at no cost to me and no significant delay. Have not been towed since (shouldn't say that too loud). Have had innumerable calls to them with tech questions and always get good tech support. When I need any kind of service, even routine maintenance they provide me with good recommendations and even make the appointments for me. I should note we travel extensively - see my name - and are seldom anywhere near the dealer we bought from.
Can't say anything about GS, never used them, but they tend to get bashed here a lot more than Coach-Net. But then again they are Good Sam.