Be warned, this is a rant, and I am probably in the top 5 biggest collectors of Koenigs, so maybe biased over here.
DEPENDS! It all depends on priority. What is most important to you; ease of opening, ease of disassembly, longevity, materials, weight, customer service (spa treatments), your particular environment of use(humid, water, sand, maybe some others I can't think of), pocket clip, lockbar insert, ease of sharpening, box presentation
Ease of opening: Arius
-Arius - has a flipper, a 'spydieflick' capability, and 'kinda' a thumb deployment, ambidextrous
-Sebenza - only thumb stud (which is extremely uncomfortable until you find you own way to open it). Some ambidextrous versions
Ease of disassembly :Arius
-Arius - uses a non-spinning pivot, backspacer screws screw direct into the backspacer(non spinning)
-Sebenza - Tolerances are the same, if not better. Way more pieces to disassemble
Longevity: Sebenza
-Sebenza - Has a proven track record, washers always out last bearings (theoretically), slower opening knives means less damage (sorta)
-Arius - Has a lockbar insert, has a better hollow grind (theoretically able to be sharpened more without losing 'sliceyness'
Materials: probably Sebenza, Don't kno much about blade materials
-Sebenza - S35vn is meant to have a ballance to be able to last in salty conditions or humid conditions
-Arius - Both use Ti
-I would suggest either way, you purchase your knife with a CF side.
Weight: Pretty similiar I think! Again get a CF side
Customer Service: Probably Sebenza
-Sebenza - proven track record
-Arius - Return might be a bit slower due to a smaller staff
Environment: Sebenza
-Especially if there's dirt and sand. Bearings attract gunk.
Pocket Clip: Arius
-Arius - Ergos are better (based on hand size), easier deployment
-Sebenza - easier putting back into pocket, screw for clip is on the outside, more grip.
Ease of sharpening: Depends on sharpening system.
-Arius - has a flat grinded edge, no thumb stud in the way
-Sebenza - Insingo blades are easier to sharpen if using a sharpening system similiar to a wicked edge, has a convex edge which is harder to replicate unless experienced.
Box presentation: Sebenza
-Sebenza - Knife, tools, lube, loctite, COA, cloth, misc.
-Arius - Knife, COA, cloth
Summary:
If you're going to buy either, you should buy one with a CF scale. I would choose an Arius, just because it's more user friendly. I think Arius' also have better ergos for a wide range of hand sizes.