I have a Kamaka tenor, a Kanilea tenor and a KoAloha Pineapple Sunday (though I have played KoAloha tenors before).
I cherish my Kamaka -- and it is the most prized possession I own. I will never be able to play well enough to justify what it means to me. It isn't the tone (which is good), or the gloss (which I have lovingly polished), or the curl in the koa (which was a major factor in me buying it). The Kamaka family is not quite as over the top in kindness as the Okami (KoAloha) family, but they have given me fantastic customer service, as well. The main reason that I prefer the Kamaka is that it is a physical representation of Hawaii for me, and the deep historical connection to the history of uke making for almost 100 years. KoAlohas and Kanileas are made in Hawaii. But a Kamaka IS Hawaii. One thing I'd like to point out in a lot of trials, when people arrive at a store and pick up a Kamaka, it has those awful stock strings on it. I don't think you can truly tell the quality of the instrument with those -- listen to some players with Kamakas and see the tone the instruments are actually capable of before you dismiss them entirely.
I don't have a KoAloha tenor (just the PS), but I have played a few of them. Most of them were strung with low g strings. I found each of them to produce great tone and fantastic volume. I think that KoAlohas are incredible instruments. I don't know if it is the process used by the Okamis, or the volume it produces, but sight and sound unseen, I would choose a KoAloha over a Kanile'a. When you add in their amazing customer service (well documented here on UU) and their cutting edge design, it is a good choice for lots of people. One thing to note, if you are traditional, they may not be for you if you want a simple, plain, conservative uke. The crown headstock and new bridge design aren't for everyone. So if your aesthetics lean towards the simple, choose one of the other two brands. But if you want volume and great tone, with wonderful customer service, choose KoAloha (like Daniel Ho, Herb Ohta Jr., Brittni Paiva and others have).
To be totally honest with you, I only keep my Kanile'a at this point for sentimental reasons. I adore Joe and Kristen Souza, and it was my first "real" ukulele. But it just can't compete tonally with my KoAloha or Kamaka. Where it does have them beat is in the finish (the UV finish is exquisite), but that is not the real reason to buy an ukulele. I have tried lots of string combinations on it but it doesn't match the depth of the Kamaka or the volume of a KoAloha. That being said, they do make wonderful instruments, after all, Aldrine uses them. But for me, while it is wonderful it is just slightly less in consistent quality than the other two brands you mention. Perhaps I just have a lesser uke, as there are tons of people on UU who swear by Kanilea. Among them Lori, bbycrts, Aldrine and others. Don't get me wrong, they are wonderful, just to my ear I prefer the Kamaka and KoAloha options. One other note, I absolutely hate bridge pins. And Kanile'as come with bridge pins...
No matter what though you can't go wrong. I think it is like the difference between a Mercedes/BMW/Porsche, or Heidi Klum/Halle Berry/Eva Longoria (or Brad Pitt/George Clooney/Hugh Jackman)...or Harvard/Yale/Stanford. My point being, they are all exceptional, it just depends on your personal taste. My favorite (for me) is my Kamaka, but my recommendation to others sight and sound unseen would be the KoAloha. That being said, you will get just as many people telling you it should absolutely be a Kamaka or a Kanilea.
A video you may want to watch is from Hawaii Music Supply where they compare a Ko'olau, Kamaka and Kanilea tenor (sorry no KoAloha tenor in that one) -- though he is doing this trial with all stock strings (including the icky Kamaka strings).
http://www.youtube.com/watch?v=2dOmCRnplQo&feature=player_embedded