After having mixed experiences with Aquila nylgut strings (both "nylgut", "bio nylon", "new nylgut", and what have you), I have found the Risa Premium strings to be the holy grail of fluorocarbon ukulele strings.
While these strings would suit any ukulele from soprano to tenor, they work particularly well with Risa's own solid instruments, which produce a tension which might (and in my case, did) break other brands of fluorocarbon strings.
The tone, sustain, and sheer looks (they're dark brown) of the strings blew me away. Once you've given them a couple of days to settle down, these strings simply do not go out of tune.
Finally, don't be put off by the price. While they go for roughly twice the price of other good string sets, be aware that these strings are extra long, which you can then cut down to your preferred size. I measured enough string to cover at least two sets of tenor scaled ukuleles, so twice the price / twice the length = an amazing bargain.
I don't think I'll be buying any other strings for my ukes in the future. They're simply that good. If you're like me, believe me, your search for uke strings is finally over.