first question - which one feels better in hand?
second - what are you planning to do with the knife?
the TAK1 has the shortest blade of the 3, but a full tang. The other 2 are hidden tang.
all 3 are coated high carbon steel.
mark 3 probably has the "grippiest" handle, due to being a rubber-like material.
I used to own an actual Ka-Bar USMC knife, but never used it, so gave it to a buddy who carried one in the service and wanted another.
I don't particularly like the way the Spec Plus handles fit my hand.
I really like the way the TAK1 fits -- but I have big paws.
Another one you might consider would be the Ontario Freedom Fighter 17 - a modern remake of the WWII quartermaster knife with steel butt cap for hammering and a rubber grip shaped like the stacked leather washers of the Ka-Bar. (Google Ontario FF17 if curious)