It is hard to quantify what you mean by "best" because it is not measurable.
Do you mean the longest life between polishing or the smallest striations on the just compacted conductor and thus the smallest amount of aluminum dust generated?
In any event, the information following this will help you make an informed decision or at least give you the ammunition to ask the right questions to the various die suppliers.
Polycrystalline diamond has highly predictable die wear and thermal stability with high resistance to fracture. These characteristics provide cost efficiency with reduced downtime.
Polycrystalline diamond is manufactured by forming a mass of diamond crystals (powder) and then applying a combination of heat and pressure. By this process, the mass becomes a single unit with the diamond particles inter-grown to each other. The final product is extremely wear resistant, maintains tight hole tolerances, and provides a good surface finish. High polish is a basic component of the standard process when drawing ferrous or nonferrous wire, including aluminum, copper and stainless steel. It’s also the perfect material for stranding, bunching, tube drawing and shaped dies.
Diamond Size Micron Size* Grade Stamping
0 - 4 Ultra U 5 - 12 Fine F 20 & Larger Coarse C
* Information provided by: -- DeBeers Industrial Diamond Division - Syndie -- General Electric Company, USA - Compax -- Sumitomo Electric Industries Ltd. - Sumidia®
You can find a list of polycrystalline die suppliers here www.wirenet.org/vts/vts_search.cfm Just select dies-diamond, synthetic. There are 76 die suppliers listed, most with web pages.