You're looking at concerts I take it. It's nice to see someone looking for a first uke that is willing and able to spend more than a hundred bucks. Among you're choices in that kind of price range, I don't think you're really going to go wrong with any. It's going to be down to options and the subtle differences of different makes.
I'm unfamiliar with Larivee, but I have read some good things about them as I'm sure you have too. Since they're discontinued, might be a good future investment.
JumpingFlea on here just traded a dud
G-String in for a Ko'olau and he'd be a good place to get some impressions on those.
I've got a Kanile'a built concert (It's branded Lanikai, but is essentially an early K-1. there's threads about that.) and a Koaloha concert (from 2000 before the musubi soundholes) Both are very excellent instruments and play wonderfully and sound great. In essence it's sort of like a decision between Fender and Gibson. It'll be down to personal preference.
The difference between the two are subtle. I think the Kanile'a one has a deeper fuller more complex tone. (This one is a great for recording.) Slightly wider neck which is great for fingerstyle playing (which is what I do) and The UV finish is lovely and seems really solid. It's a little heavier but since I prefer to play seated, that's not a problem. My
only complaint with it is that the end of the fretboard right above the sound hole is straight across rather than tapered so I tend to catch my thumb on corner of it when I play. It feels built to last and I can only imagine it sounding better over time and probably becoming more sought after. The sound of it still makes me pause every once in a while. It's just gorgeous. This is the one I'd use if I ever had to demonstrate to an unbeliever what a ukulele can be and sound like.
The Koaloha is perhaps a quarter inch shallower in the body and has a really bright, spritely and louder tone than it's counterpart. Super light. One piece top and back and a koa neck. (don't know if they still do that.) Neck is thinner in profile and across. The end of the fretboard is nicely scalloped and perhaps it's an illusion but it feels like the frets are spaced a little further apart and the bridge a touch further back. The fretboard feels really wide open and fast. It's a wonderful player's instrument with a good presence in jam session situation. It's the one I seem to grab a little more often than the Kanile'a just because of how it plays. It's got tuning pegs as opposed to geared tuners which have a slight curve to using at first. Overall the finish and wood isn't quite as dramatic as the other, but Koaloha does have a lot of little touches like their headstock and the musubi soundhole and the way they scallop end of the fretboard that set them apart. A player's instrument.
If you do a quick Youtube search you should find more than a few reviews and samples to watch. I know UU member Ken Middleton has done a super review of his Kanile'a and there's factory tours for both on there that are quite amusing.
that's my two cents on what I can offer. I'll go and make some more espresso now. That's a lot of typing and thinking when you're undercaffeinated.