I'm a moderator at Ukulele Underground. I agree with Tootler, it's a great place to get information.

There are many great 'ukuleles available at great prices - Kala, Lanikai, Pono... All fine, but not the equivalent of Taylor or Martin guitars. Martin ukes are great, but not everyone's preference. Certainly the Hawaiian people tend to prefer 'K' brands made on the islands.

The Collings ukes have an absolutely stellar reputation (as do all their instruments). If you have the money you couldn't go wrong. If not then try out the models you can get access to in a shop within travelling distance.

Moving from guitar I'd recommend trying concert and tenor sizes in particular. Just my personal opinion, but bari just doesn't feel ukey enough and I find soprano a tiny bit too tiny.

'Ukulele is a great instrument.