Generally speaking, going with a thinner string of the same material will produce a brighter, less full, sound. In the guitar world, lighter gauge string sets have a thinner sound than heavier gauge sets. It is similar with fluorocarbon ukulele strings, although I'm sure there are some nuances between manufactures. The easiest way to keep things straight, at least for me, is to know the string diameters. Blindly buying sets can become costly especially if you end up mixing and matching strings.

For example, Oasis Warm and Brights differ because the A and G strings are different diameters. The C and E are the same strings (at least a couple years ago when I measured them). For me, the problem strings (re-entrant tuning) are the C and A strings. Getting the right dynamic between too thin a sound, to too much boom, too a choked out sustain is a balancing act. Low G has to be the toughest to balance out.

What Robert brought up is correct. There are string combinations that will bring out great tones, but they need to fit into a small tension range for the soundboard. For me, knowing gauges does help to guide me to some degree. Although, I have not figured out why there are tonal differences between Worth Brown and Clear for the same gauges. I've just chucked it up to chemical differences in manufacturing.

John