What is your definition of "best"? Best = highest quality? Best = makes most accurate ammo? Best = finest tolerance? Best = ......etc etc.
IF your question is based on getting dies that create ammo that fits your gun perfectly, then it depends on the ammo and the firearm it is being shot in. Most of my die boxes are green or gray. RCBS has a good reputation for quality and warranty. Redding also has a good reputation for quality, warranty, and availability of specialty dies. I also have Hornady, Lee, Lyman, Dillon, and a few others. I find that most companies are cognizant of these chat forums and are either monitoring, or occasionally searching, for comments related to their reputation. Within the last 30 days, I have had warranty replacement parts from Lee and Dillon. Was their product bad....no, operator error, but they both stood behind their product.
I find that as I develop into a better shooter and better reloader, my taste in gun quality is going up and my craving for better accuracy is going up. When I first started shooting some of my guns, the "best" dies were the ones I could afford, or the ones I could find. They were best for me because they allowed me to shoot my firearms with reloaded ammunition. As I get into better quality firearms, tighter tolerances, match specifications, etc, it takes a better quality die to match the quality of my firearm. The "best" dies are the next higher level to match the higher level firearm.
Caddilac dies will not make a VW firearm shoot like a Caddilac firearm. Chevy, Ford, or Dodge all make dependable cars, but we each have a preference on which we feel is "best" for us. It is not until you get into more specialized sport like dirt track racing, circle track racing, drag racing, or stock car racing that you find you need a more specialized car. Shooting is similar. Pick your Chevy, Ford, or Dodge dies to start. As you find you need a more specialize gun, get the more specialized dies. The dies you choose will only be the "best" when they can create ammunition capable of achieving the best accuracy out of your firearm.
My novel response on dies.......