Ko'olua Gold concerts tryin those on my Soprano KA-S and they sound very nice.
Aquilla's
D'Addario Pro-Arte's (stay away from the Hawaiian/Concert pack)
You'll need to get all the different strings you can and play them for a couple of weeks then change them till YOU find the sound/feel that works for you. and while your at it...
Get another of the same Uke so you can test the strings against each other!!!!!