Best knive metal?

[budgy]

I reckon you should be posting the question to the knife makers guild. Unfortunatly salt water and high carbon steels don't mix. Stainless doesn't hold as good an edge and sub zero quenched 440 is hard to resharpen. Never tried stellite but then its probably to brittle. The Victorinox paring knife is a pretty good choice, straight or serrated. With a little work the steel can take an edge good enough to shave the hair off your arm and its easy to re-sharpen. For cheap knifes Opinel is one of my favourites.

 

[ScubaRon]

While I strongly recommend you carry a knife or other cutting tool UW it will be the least used piece of gear in your bag. Just get the cheapest SS knife/shears and spend your extra money on a better BC/regulator/fins/mask or whatever...
ScubaRon

 

[Akula]

Titanium of course. The more expensive the better. That way I can stop finding cheap corroded stainless blades on the bottom.