I've bought two of my Kamakas online, sight unseen; another in person but without others to compare it to; and the most recent one (the pineapple) in person with a choice of two different ukes. And while I doubt that one can go wrong with a Kamaka in general, I will say that the difference between the two pineapples I compared was really dramatic. The one I bought had a much brighter, more bell-like tone than the one I passed on, which sounded more muted and mellow. Both sounded quite nice, but I was able to pick the one that had the sound I liked best. So, there's a "pro" for buying in person from a store and paying a bit more (which I opted to do, since sales tax alone added 10% to the cost!).
On the other hand - when you buy by mail, you don't have a basis for comparison. I'm pretty sure that with an instrument like a Kamaka, you will be happy with whatever you get.
As for which store to buy from - I might be mistaken, but when I was shopping around for a pineapple I think PuaPua marked the price up a bit from Kamaka, and shipping was higher. But as others have mentioned, you will probably be able to get photos of the uke, maybe have someone send a sound sample or play it over the phone for you, etc. I know with Kamaka, you place your order and a month or so later, "your" uke pops off the assembly line and it is what it is - you don't have others to choose from, and I'm pretty sure that you won't get pictures in advance. Even in person at the factory, you can't pick out a uke - you can only place an order.
I haven't bought from Hawaii Music Supply but a friend has, and she had a great experience with them - she didn't have any idea what uke she wanted (her first) and they helped make a great choice for her.
That being said, Kamaka's customer service has always been good to great in my experience. I recently ordered a pineapple case from them,, and even though it was only a $30 purchase the service was excellent.
Also, check out this
list of Kamaka retailers, there are a few other dealers that I've heard good things about: Acoustic Vibes, Gryphon, and Artisan Guitars are a few that I recall hearing about.
I'm pretty sure that whichever way you decide to buy your pineapple, you will LOVE it. Mine quickly became my favorite uke. even though I was convinced that I didn't like playing sopranos nearly as much as concert ukes.