In my opinion, the best soldering iron tip material is:

The soldering iron tip is composed of five metal materials: copper, iron, nickel, chromium, and tin, of which copper accounts for about 85%. The inside of the external heating soldering iron head is pure copper and the outside is iron alloy for protection. Internally heated soldering iron tips are generally made of copper with Ni alloy plating on the surface. Electric soldering irons are divided into two types: external heating type and internal heating type. The soldering iron head is a supporting product. The material is copper and the basic shapes are sharp, horseshoe, flat and knife edge.