I had a KZ travel trailer for about 6 years. I would describe it as "middle of the pack" in terms of quality. When it got to the point where I was spending as much time fixing it as using it - it was time to sell. I've never heard a significant number of complaints about KZ not standing behind their warranty.
From what I've read recently I would say that that a lot of Grand Design owners are satisfied with their RVs and how well the company stands behind the product. Ultimately I would go with the floor plan you like best. Good luck with your decision.