I think my vote has to go with the Retro 7 too. I have one already, and a Gen3 paid for with a full slide kit and mag changer. I think that will be the ultimate SC marker for "Duck Aficionados" given the way they're designed.
Out of the Redux, VKC duck, and Kamikaze Duck, the Redux has always been my favorite. Once i did the anti-pinch mod on the slide, it's been one of the few guns I have that has never let me down. I get solid efficiency out of it, it shoots where I point it, and it just looks good.
The Kamikaze Shooter was my dream gun, and has become a bit of a wallhanger. I still bring it out once in a while, but I'm very selective about it. Usually only on low key walkon days, or games where there's a good amount of fellow MCB'ers.
The VKC Duck is the black sheep. I want to love it. I want it to be the best of the three. It simply does not pinch. I pulled 30 shots out with the standard short barrel. It's two tone dust/polished finish is beautiful. But the biggest flaw with it is the snub underneath the slide. The slot that the bolt latch goes through is milled too long, and presents some issues when you air it up. If you're careful, delicate, and precise, it's not an issue. But when you're getting shot at by three people with Egos, it's a problem. The slide can travel too far back, and pop the valve open when you pump it. I've sent paint downrange several times just pumping the thing. But, I won't get too into it because it irks me and I can rant about it all day.
Bottom line/TL;DR - Retro 7. Especially with the slide kit. I think it's going to be the best of the bunch.