The "best" extended warranty might be zealous maintenance. Beyond that it kinda depends on whether you want to "self insure" (if it breaks, you pay) or not. If a costly repair bill jeopardizes your financial security or has a huge impact on your life, then by all means get the coverage. OTOH, diesel engines, for the most part, are very reliable (there are millions on the road all the time)... as are most of the parts on a MH, individually. There's also the deductible, how likely are you to have a really expensive failure? I don't know the statistics but, like you say, it is a fairly complex system.
Risk is very interesting... if you take the cost of the extended warranty and bet it all on BlackJack in Vegas, or roulette... you have about a 45% chance of doubling your money betting conservatively, yet you can see that gambling is very profitable for the casinos. Same thing for the warranty company... it is just harder to see what they do with their "winnings".
If you take the money you would have spent on the warranty and buy a CD, you get, maybe 2% ROI, guaranteed. Not very attractive. Maybe in these economic times, extended warranties are a better deal? Especially if you plan to drive a lot and use the vehicle often. If CDs were paying 12%, they'd double your money every 6 years. After a while you'd have a "nestegg" to pay for repairs forever.
Please share your decision and rationale...