I own a Koolau and a Kanilea. I have been to Hawaii a few times since I started my uke interest and test drove tons of ukes but really I don't know what I'm talking about and I'm not much beyond a beginner player, so... grain of salt...
Koolau: I've only played one, and that's the one I own. I bought it second-hand right after I decided that ukulele was more than just a passing fancy. It's beautiful, it has some heft to it and feels to me like a more "professional grade" instrument than any other uke I've played. I have it strung low g and it's a tenor, so it has a very warm mellow sound, not as "twinkly" or "sparkly" as most that I've played (I also mostly play concerts, so that's part of it)
Kanilea: Best looking of the main 3 by a long shot. Most modern look and fanciest Koa. Some people value looks more than others. I definitely consider looks as important and I think a lot of it is because I'm not a great player and a nice looking uke makes me more likely to pick it up. I would guess that people who have played for decades care more about the sound and don't care if it looks like a dirty sock. Very sweet sound, tending to be more mellow than the others.
Koaloha: I don't care much for the looks but the sound is very attractive when comparing it to the others because it really pops. The instruments feel light weight and project like crazy. I understand why people like these and maybe if I was a better player, I would be more interested. I almost bought one once but went with something else that I felt had more interesting character (no regrets).
Kamaka: The classic. Some people love that it's the classic and it's like a piece of history. It's never the wrong choice, but for me, it's never the right choice either because they just never seem to have that something special that makes me want to pick it up.
Overall, Kanilea is my choice but I also JUST bought one. Ask again in a year and I'll probably have a different answer.
