I tend to favor what is easiest to clean because sand is so...sandy. So to me, a H1 fixed blade is a great marine use knife.
From my experience, frame locks are generally the easiest to clean of folders when sand is involved, and everything else is generally more of a pain. In most instances, the action of the knife is going to get gritty if it's buried or used to dig in the sand. In the category of ease of basic and detailed cleaning, the open frame lock is hard to beat. The compression lock on the PM2 is right there with it. Both styles can also be hit with a compressed blast cleaner pretty easily, but I personally find that once sand gets into the pivot/washer areas that the knife needs a full strip and cleaning to get back to 100% factory smoothness as the sand tends to be hard to get out.
If rust is a huge factor, H1 seems to be hard to beat. But all of the steels you mentioned have corrosion resistance in which if you clean them properly after saltwater usage, you should not have any issue. If you are really worried about rust, treat them with a protective coating before usage, although this is not necessary.