High-speed steel (HSS) end mills are cost-effective and suitable for general-purpose milling applications. We recommend HSS end mills for softer materials and less aggressive cutting parameters. Cobalt end mills, which contain a higher percentage of cobalt, provide increased hardness and wear resistance. This makes them suitable for more challenging materials like stainless steel and hardened alloys. We suggest using cobalt end mills when facing rigid materials or looking for increased tool life.