Hi nathanbgilliam,
Post #12 here along with post #6 here has information about wool quilting vs a stretch knit cover.
The durability of a cover would depend more on the type and thickness of the fabric more than whether it was quilted or not but if everything else was equal I’d probably give the edge to a quilted cover (which has two layers of fabric and the wool in between). If you are comparing two good quality covers though neither would have a durability issue. On the other hand a thin unquilted cover that used a lower quality cheaper fabric would certainly wear out faster than one that used a higher quality more durable material.
Phoenix