Grand Designs manufacturer support is outstanding, as I am familiar with it knowing about a friends Grand Design 5th wheel that had to be returned to the factory twice for axle, leveler, and frame issues, and once they sent people to his location since he was close to them.
If warranty service is your concern you're still going to be at the dealers mercy and schedule. I have talked with Grand Design owners who told me they have an agreement with dealers that the Grand Design buyer comes first. Since most dealers also carry other brands, I have to call BS on those claims. One would think other manufacturers associated with a dealer would have a huge hissy if one of their dealers was providing different levels of warranty service to another brand. I know that the dealer where we purchased our Rockwood from, who also hawks Grand Design, you're going to wait weeks if not months for an appointment and the actual work may take just as long. All buyers are treated equally.
All of that said I looked over my friends closely, and have looked at many on lots and at shows. I see no difference in materials, workmanship, and methods from a lot of other brands. Plenty of loose trim, sloppy cuts, spaghetti wiring, sloppy work in general. And like most others lots of Lippert...maybe more than average.
I would not get brand fixated. I would find a floorplan we wanted, then the manufacturers who made it or similar, then look at different brands. Then look at different units of the same model/floorplan. Units can pop out of those factory doors an hour apart. The first could be almost perfect, the second an absolute joke and a POS.
I would steer away from ordering from the factory....I found that to be a huge crapshoot as to what you get handed, or what they attempt to hand to you. If I cant see the unit I am actually buying, I am not buying, so ordering can become a months long process, as in 6-8-10 months, especially when you refuse to purchase the one that arrives with your name on it because its a POS. I could write a 10000 word essay on how that works.