get a separate knife and marlinespike. I find the blade gets a lot more use than the spike, and I only use a spike when I splice large diameter line that is too tightly laid to open with just my hands.
I prefer plain edge. serrated works good on modern synthetic lines when there is a strain on the line, but for plain push and pull cutting, plain edge is safer. I prefer a point, but a lot of people are afraid of points on a pitching deck.
depending on what you are wearing (shorts, foul weather gear, all bundled up, etc...) should determine the knife. I found the Myerchin large folder to be too heavy (heaver than a 110) for shorts. a sheath knife is good, and most sailor's sheath knives come with a separate marlinespike/shackle opener.
I like a folder with a clip personally. it goes with anything, and if they are light enough, you can carry several. I like one IWB, one in my pullover or oilskin jacket pocket or clipped to the bib of my oilskins, and a fixed blade, or open folder on top of the lobster tank or in a lobster tray.
most stainless steels will remain relatively rust free if given a minimal amount of care. 440C (myerchin) VG-10 (spyderco Salt series) H-1 (Spyderco, Benchmade 100H2O) all have high corrosion resistance.
I don't know about the boye folders, since I havent gotten around to getting one yet, but myerchin and spyderco would top my list.
I keep a pacific salt iwb in case i go overboard, and my main using knife is still on deck.
but if you are looking for a stain free locking folder, get an atlantic salt, or even a spyderco rescue will stay relatively stain free in vg-10. A separate marlinespike can be had for about twelve bucks, and a screwdriver suffices in a pinch.
Pete