Anyone besides me admire the elegance of Walter's solution? Just buy 'em both!
It's almost meaningless to ask which is "best" without saying exactly what it's best for. I'll assume you're talking about everyday utility use, with perhaps hard defensive use as a backup role.
The blade on the CQC6 is a chisel-ground tanto blade. Cuts like you won't believe, but for utility use, it won't cut straight. And I dislike not having a belly for utility use. On the other hand, the Sebenza's blade shape is outstanding for utility, nice point, plenty of belly. The high hollow grind cuts incredibly well.
I don't particularly love the handles on either knife. The CQC6's handle is much bigger and beefier, which is both a positive and a negative. Positive due to strength and hand-filling for good a good grip. But also negative because you're carrying around the huge handle, with just a 3.25" blade inside. The Sebenza's handle size better matches the blade size, but is not the big hand-filling handle the CQC6's is.
Lastly, the lock. My experience with Emerson's liner locks, both custom and in the production line, has left me feeling they're hit or miss. Hopefully you'll get one with a good solid lock. The Sebenza's lock is one of the best in the world, a superb design, brilliantly executed.
My CQC6 stays in the case. It's just too much handle to carry around for too little blade, and I just dislike chisel-ground tantos for my utility uses. I don't have a Sebenza, but the type of knives I favor much more resemble the Sebenza. If I had one, I would no doubt carry it a lot.
Joe
jat@cup.hp.com