The 4 die set with the Lee Factory Crimp die is the best combination I have found. It does take an extra step though unless you have a progressive press with at least four die holes. For me it's well worth the extra step because the Factory Crimp die does a final sizing of the completed cartridge to guarantee a proper fit in the chamber. The 3 die set will work fine on 9mm but you do need at least 3 dies, one to size and decap, one to expand and bell the case mouth for the bullet, and one to set the bullet (and crimp if you don't use the 4th die). I would recommend you buy the 4 die set because you can use just 3 of the dies when you want to work faster and use the 4th when you want to be sure your cartridges are perfectly sized.