Hi,
I've owned Commanders in the past, and owned (own currently) multiple large Sebenzas primarily for utility and secondly for defense. I have only handled the AFCK series and can't really comment on the cutting ability (but otherwise have a lot of background experience with owning BM knives)
I think that the Commanders are a a nicely designed knife, but to compare to the Sebenza might be a case of apples to oranges. I felt the Commanders I've owned are basically on par with Benchmade knives, in terms of fit and finish, but a wee bit pricier. The wave feature is neat, and I'm sort of surprised not to see it as an option on all of Mr Emerson's production line (i've seen the limited versions of his other knives with the wave feature, but i would consider those and exception) The Sebenza on the otherhand, is the priciest of the bunch (though you could get a second hand one for maybe the retail of a Commander) The Sebenza has a great stout utility blade, and takes an extremely sharp edge (literally filleting paper). I don't have any complaints about the knife, but I would say that it wouldn't do as well (perhaps) in a knife fight, given the small amount of the handle you can really get a good grip on. The Commander has a better designed handle for penetration, though like the previous posters have mentioned, the belly may hurt it's ability to penetrate overall. With the Sebenza, not getting a good grip on it might have you ending up with a fistful of blood if you slipped. Looking at the AFCK and Commander reveal to me a different emphasis on their design (and considering the names and purposes) With their ability to get a strong grip and not worrying about having your hand slide up onto the blade.
I've also owned two custom Crawford Kasper folding knives, and though I found Mr Crawford to be a little disagreeable, the Kasper design lends itself incredibly well to what its meant for. The grip is a no brainer, you don't have you reposition your hand in any way once you grip the knife, it sort of grips you back the way its designed, with the grooves and built in guard. My complaint about the custom models, was the variations in the quality of grind on thumb ramps and minor finish problems I've seen in the onces I've owned. I can understand and accept them from the standpoint of a custom enthusiast, but find it more unacceptable that a knife maker of reputable background wouldn't correct something he had done poorly (email me for more info, it's a short story).
I think that the CRKT Kasper is a nice affordable translation of the custom KFF, though I wish they spent a little more money on the materials used, like someone else said, the steel in the CRKT variation of the KFF (AUS6 or 8?) would never outcut the D2 in the AFCK.
So to recap
knife=primary/secondary
Commander=defense/utility, leaning towards defense
Kasper=defense/utility, heavily leaning towards defense
Sebenza=utility/defense, leaning towards utility
AFCK=a nice inbetween, straddling the line
so...
just my 2, everyone has their own opinion and thats all this is.
jon