I got the large seb 21 first and I thoroughly enjoyed it but it didnt WOW me, probably because I had a Bradley Alias2 first and it is every bit as smooth as the sebenza. Sebenza is a nicer slicer though. I just recently got a Strider SnG with double gunner grips and a digicamo blade. Now that thing made my eyes light up and go wow. I am NOT saying it is better, I just havent had a knife like the strider and had similar knives to the sebenza. Go with your gut and know that is doesnt matter because in a couple days or weeks you will buy the other.
In less than a month I have bought 2 large 21's traded them both, have a small 21 coming tomorrow (will probably sell or trade it) because I just bought a small 21 micarta inlays today. Oh and dont forget the strider purchase I made last week. Sooo yeahhh.
Maybe get the seb first because it can be used anywhere and everywhere, the strider for some people is more of a certain duty kind of thing. If I wasnt trying to trade my SnG it would be in my pocket every day.