Each is tiny, unobtrusive and sudden death to monofilament while presenting no danger to hoses or fingers. The best tool for dealing with lines, nets and what have you may be paramedic's shears, such as the Sea Snips from Sport Divers, Innovative Scuba Concepts and others. They rip through nearly anything, even half-inch nylon anchor line, in one snip. Of course they may require you to change your self-image from slayer of great beasts to underwater seamstress. If that bothers you, maybe Jenny Jones can help.
Stainless steel comes in many flavors.
Edges may be straight or serrated. Many knives have both. Serrated edges cut kelp and natural fibers better, but coarse serration will just snag small line instead of cutting it. On the other hand, a 400-series knife will stay sharp longer but may break if used as a pry bar. No stainless steel knife is truly rustproof or maintenance-free, so it's a question of what kind of maintenance you want to do.