I've heard good reviews about this one. and the dealers will accept most of the warranties as long as the service adviser you're dealing with is nice enough.
You see, the only role the warranty plays is to pay the dealer rather than you paying out of pocket. But for that the service adviser has to call the warranty company, give your warranty info and get an authorization before performing the work. As long as that's done by the service dept. you'll be good to go. next step would be for the warranty to accept the work that is being done as being "covered" under their policy.
Mostly I've seen independent mechanics giving problems with extended warranty because the warranty only pays them by the book. meaning the mech's can't rip you off with extra labor or costly parts. But the dealerships usually are OK with the extended warranty companies.
Do an online search and see which ones give you most coverage. As I said, people I've spoken to gave good reviews for this one :
but then again it all depends upon the car that is being covered and the nature of the work that had to be done on their cars.
Good luck !