Strings are very subjective, so the best thing is to try as many as you can and decide for yourself what sounds best on your uke.
Generally, they aren't that expensive, so it's not to bad to try different brands out. You will no doubt see suggestions for some of the following. These seem to be the more popular brands, South Coast strings, Savarez, Oasis, Worth, PhD, Living Water, D'Addario, Martin and Fremont. Flourocarbon strings generally will yield a brighter sound than nylon strings, but some don't like the thinner diameter or the density/tension of fluorocarbon.
Again, try as many as you can and decide for yourself. There are a lot of threads on strings here, so if you do a search you will find a ton of info on them.