Aside from perusing their webpage, I'm not up on Jayco anymore. Grand Design has the cleverer designers, and their layouts and features have been copied by nearly everyone.
As clever as I believe GD to be, I'm not as impressed with their construction. They are manufactured with OSB, which is probably not a big deal unless you spring a leak. Fit and finish has been less than stellar when I've window shopped them over the last few years. Surprisingly this last year hasn't been as bad. The larger tanks are important to us.
Between those two, I would likely select GD, but as noted the dealer is an important part of the equation.
JMHO of course.