I have a Kanile'a and love it - it's the current design with the TRU bracing - don't know if it really makes a difference or not, as I've not compared the older design in a soprano (though my concert Kanile'a is pre-TRU bracing and it's wonderful, too). Anyway, it's quite loud and has a gorgeous sound with sustain that really surprises me in such a little instrument.
You're not really going to get a helpful answer here - both Kanile'a and Koaloha are terrific instruments (can't really say much about Honu, though I've heard great things about them, too), so the difference really just comes down to individual preference. If there is any way to try all three out, you really should. I don't think you could go wrong with any of them, and I think you'd be very happy with any, but if it's really bugging at you, then see if you can try all three...