I cant say that I know which supplier would have the best quality leaf spring, I bought mine (like new used) so did not shop around. One thing I do know to look for though, is more leafs, that are thinner. This indicates that higher quality steel has been used. As far as the rest of your suspension products, I would suggest going with BDS. They have quality products, and an excellent warranty, not to mention cust service that is unbeatable. I would choose this supplier but my Jeep is too old!
Consider greasable bushings to increase the life of your springs.