I've compared Shimano and Joytech freehubs dimensionally and found that the 7s Joytech hub was a bit heavier and didn't position the driveside flange as favorably as the Shimano freehub.
But I have to say that it was a small difference, and that Joytech cup/cone hubs seem to be of very good quality otherwise, with very smooth bearings that (like Shimano's) can last a very long time.

Hub bearings fail most often because they are installed on bikes with their bearing adjustment having no free-play, so when the axle shortens as the QR lever is secured, the bearings go quite over-tight. Some cup/cone hubs do survive such abuse better than others, but it's entirely avoidable by loosening the bearing adjustment when the hub is still new.
Rust is another common cause of failure of bearing surfaces, so axle cone sealing quality can be very important as well.