It seems as if this subject was bound to be asked eventually (if it hasn't already in the past
. I currently have a Benchmade on a carabiner hanging from my tramp. It's a lower (griptilian I think) model with an Americanized tanto tip (I'd prefer a clip point or drop point but it was a gift). I prefer for all my knives to be half serrated since I believe it is more versatile. Now that being said, a marine knife was historically one with a marlin spike built in. Someone posted one with a locking spike which I think I will think about purchasing in the future(Myerchin Lightknife Crew Pro). I would not get any knife without a lock of some sort (Benchmade is the self proclaimed strongest lock in the industry, and I for one believe them) b/c the knife can fold over on your fingers (my swiss army knife did it all the time as a kid). My brother has a Model 710 McHenry & Williams by Benchmade and I think that could be the best knife I've EVER used/seen. But it's a bit pricey (almost $200). I have an early Smith and Wesson that is really solid but the later ones I've seen are terrible (I think they had a company design them and produced them for a short time, then outsourced them to China).
On Leathermans, I say they are the best multi-tool ever devised. Gerber multi-tools suck. My grandfather uses his multi-tool on a regular basis (many times a day) and he broke two Gerbers in about 3 months. Then he went back to Leatherman and he's been happy ever since (although he does wear them out about every 2-3 years also, using them for things they weren't designed for). I carry a Leatherman squirt in my pocket everyday and I've have 4 other different Leatherman multi-tools. I had a Leatherman original, lost it, bought another original version 2, found the first, wanted a larger Supertool, had that for about 5 years, wore it out (it still works I just chewed up the cutters cutting HUGE wire and broke the phillips screwdriver off trying to pry with it), then bought another Supertool 300 and I've had it ever since. Several friends of mine have the Wave and like it a lot for the one handed knife opening feature. If I get another one I will get a Surge (larger Heavy Duty Wave). There is a lanyard ring built into every Wave and Surge. But they are heavy. Leathermans are ok for shackles but the pliers chew up the shackles if you're not careful. Frankly a claw hammer or better yet a adjustable wrench is probably better for shackles.
If you plan on getting a fixed blade knife just be certain you get a really solid sheath. I've hear stories of people buying knives with cheap sheaths and the knife pokes through the sheath and can hurt someone. Although it doesn't really feel great on your belt the plastic/kydex/polymer sheaths are very safe. Otherwise a very stiff leather is vital in my opinion.
My next purchase will be a Hobie tool I think for the shackles and the rudders. I too have had to use the main sheet to pop the rudder cams loose and it is generally not very fun.