Great timing, as I've just recently switched strings on my Kamaka baritone, D'addario Nyltech to Aquila Nylgut.
The Aquilas have settled down nicely in the 2-3 weeks.
My experience is as the others have stated.
Nyltech:
higher tension, thicker feeling, warmer rounder tone than the Aquila.
However, less sustain and a slightly "muted" feeling, at least on the particular uke I used it on. Very much of a "classical guitar" like sound. Here is a video with my Kamaka baritone with the Nyltech strings:
http://www.youtube.com/watch?v=R9NoiL3fmcg
Nylgut:
lower tension, thinner strings. But it gave out a brighter, more open sound than the Nyltech.
However, I'm not sure if I'm liking the lower tension - it makes me have to hold back a bit from strumming as hard as I want.
I found the Nyltech's better for fingerpicking instrumental songs.
But I find the Aquilas better for accompanying singing in our church group meeting. The strums sound more alive with the Aquila, whereas the fingerpicking sounds more alive with the Nyltech.
I might have to change strings again soon though. Not entirely happy with the Aquilas on this particular uke. I'm contemplating on giving the Guadalupe Baritone (normal DGBE tuning) they have available at Mainland a shot.