Best Drill Bits for Metal: Our Top 5 Picks. Best for Hardened Steel: Drill America D/A29J-CO-PC Cobalt Drill Bit Set. Most Versatile: BOSCH BL21A Black Oxide Metal Drill Bit Set. Best for Stainless Steel: Cobalt Alloy Steel Drill Bit Set. Best Step Drill Bits: IRWIN Step Drill Bit Set.