I suppose it all comes down to personal preference, although some might argue that the thicker finish for gloss could impair the wood's sound qualities. It also shows fingerprints and should be wiped down after playing.
Personally, I prefer a natural/matte finish, although I do like my Mainland red cedar glossy tenor a lot.
I got a concert mainland in glossy. I love how the grain of the wood comes to life. I also like being able to wipe it off with a soft cloth and have it come clean easier. I also think the gloss protects the wood a little more but I might be deluding myself in that.
Glossy is really pretty...and shoes strum marks really bad. And fingerprints. An unless I am ukin' in the nude, they are slippery too- I totally prefer satin. It is not as durable and not as pretty, but it is easy to hang on to
my first uke was gloss, so the second one had to be matte to be able to acompare them.
the differece i feel is that matte has a bit more high end, tiny noticable but is there.
second, i touch a lot the uku while i'm playing, includding the nail tapping technique from the flamenco, all these sound are more noticeable with the matte finish