What do you mean by "best". Do you mean cheapest?, strongest?, best value?

440Source is usually the cheapest. SCAT has rotating assemblies with a Mahle piston which I think is better than the ICON piston that 440Source uses. You can also get a K1, JE combo which works really well. Lots of choices.

Instead of asking for best you should tell us what you're trying to do. What heads do you have? What compression ratio do you want to run? What bore size? How deep do the valve pockets need to be?