Be aware that there's a trade off between toughness and hardness with cutting materials. A harder/ faster cutting tool (spot weld, lathe, drill whatever) is often more brittle and more likely to break under shock.

If you can get a tungsten carbide drill bit it'll be hard as and be able to cut fast but once it's blunt or chipped you'll likely have to throw it away. If you can sharpen them yourself I think you're best off with a good quality high speed steel (carbon steel), especially if you're drilling with a hand drill.

Have a look at sutton tools, they have a decent rep. My Dad's (carpenter) still using sutton drill bits that are at least 20 years old. Their factory is just around the corner from my house to.