I would say wood on the small and micarta on the large.
The small size is good for everyday usage but is IMO also perfect for semi-casual on up to fairly formal. In khakis and dress pants it's as big as I want to carry but carries well. The wood dresses up the sebenza in a very classy way.
That's my only reason. YMMV
I also concur with TLR's use model and resulting opinion.
The other thing to consider is harsh moist environments. All of the wood options are reasonably moisture resistant; however, to differing degrees. I ruined the finish on my Mnandi camelthorn inlays by wearing it IWB during sweaty workouts, accidentally sending it through the wash and letting it sit in a wet pocket for a prolonged amount of time

. Cocobolo is very moisture resistant due to its natural oils that make it so (it's used on the Inyoni bird 'n' fish knife) , and of course, lignum vatae is very dense, robust stuff. As for micarta, I figure you could send it to the bottom of the ocean for a year, and it would come out lookin' great.
In conclusion, if you figure you'll be more careless (as I am) with moisture with one of your knives, I'd include cocobolo, lignum vatae, or micarta as inlay choices for that one. If you're like the majority of the Seb users out there and have the presence of mind to remove your knife before tossing it into the hamper, pick your inlay on visual appeal with no worries.
Fooj
P.S. As for my personal choice, my small Seb EDC is a classic w/ cocobolo, and my large Seb EDC is a unique graphic

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