To start, I no longer recommend liner-locks to anyone anymore, though my Military knives have been reliable. Frame-locks have similar issues as liner-locks, but are generally more reliable. Not particularly enamored with either lock type at this time.
That said...
The Military and the Skirmish are two very different knives. The blade shapes are the determining factor, IMO.
The Military is a good general use slicer due to the how thin the blade is about the edge. Yes, the tip is more fragile than some other designs, but in many situations that thinness is appreciated. The grip frame is one of the better handfilling designs. I consider the Military a light in weight, medium duty knife. The Military's design is a classic as far as modern knives go because it is so useful.
The Skirmish is also a good design. The blade is more robust than the Military's blade, but at the cost of thickness. I like the recurve and the front "belly" curve with less pronounced tip makes the Skirmish a better knife for hunting, for example. I don't find the Skirmish too heavy to carry, but I do carry IWB.
There are a plethora of other differences that can be issues when comparing between the Military and Skirmish. Do you like sharpening recurves, for example. Value a titainium handle over G10?
If I foresee food preparation, fine cutting, or simply desire a light weight, I still carry a Military occassionally. When I foresee cutting rope or woodwork, something that requires a more robust tip, I carry a Skirmish occossionally.
As for the Sebenza, that knife is better crafted than either the Military or Skirmish, but in use you'll not notice such. The Sebenza is also a classic design and very good at most cutting tasks. However, whether that better craftsmanship makes an appreciably better carry knife is up to the user. The Sebenza costs a fair bit extra over either the Military and Skirmish; in fact, you could buy one of each and still spend less than a single Sebenza.