I can't help with the coach manufacturer reputation, but I've had excellent service from my Freightliner chassis, and the free support from Freightliner is great. They have a 24/7 free help desk staffed with folks that know their product.
Regarding water in fuel, there will be a fuel filter/water separator somewhere on the chassis (located by the coach manufacturer during build). Draining a little fuel into a see through container will allow you to detect water in the fuel (I haven't found any significant amount in 12 years).
Fred