A week ago I hadn't played any of them, nr any other fancy sopranos, but that all changed on saturday when I was invited to a "soprano ukulele blind test" in stockholm! It was totally awesome (albeit a litttle nerdy perhaps...but I am a uke nerd and proud of it!).
There I got to play (if my mind serves me):
Koaloa
Kiwaya
Pete Howlett
Martin (vintage)
Gibson (vintage)
Kamaka
Kaniela
Brüko cedar
Mahalo (thrown in to confuse everybody during the blind test)
Argapa (hand made by Sven, the host of the party and UU member)
And, back to your topic, I can say that both the Koaloa and the Kiwaya struck me as awesome! The sound of the Koaloa got my vote over all the rest in the blind test, but when playing them myself I fell in love with the Kiwaya. It was pure love! So light and smoothe you hardly noticed it in your hands, and so easy to play. Although it's rather plain (exactly like an old martin), in my book it's absolutely beatiful. But then again, to Koaloa won my vote in the blind test for sweetest sound...
You can't go wrong with either one of them I think. (if your biggest problem is to choose between a Koaloa and a Kiwaya, you have a pretty sweet life...)
Cheers