For my rifle cartridges I prefer the FCD. For straight walled pistol cases, of which 40 cal is the one I load the most frequently, the Dillon is my choice.
Since I mostly shoot coated lead bullets in my 40, they are a little larger in diameter than jacketed bullets. Consequently, the FCD's little carbide ring tends to size the case down a little smaller, and this in turn mashes the lead bullets enough to cause leading in my barrel. When I use the Dillon, it only touches the case mouth, and irons out the bell introduced at the charging/belling station on my press. I get no leading when I use the Dillon taper crimper on my 40.
On both the 223 and the 308 where I often load bullets with a canellure, the Lee FCD works very well. I have not tried the Dillon taper crimper in this application as I haven't felt the need. Also the non canellured bullets don't receive a crimp in my rifle cartridges.