If it’s a Spanish or classical guitar, which uses gut strings, I can’t help, but if it uses metal strings then I think it’s better to use cheap strings and change them often to get a "crisp" ringing sound. All strings lose the higher frequency harmonics over time because they get gook from your fingers on them and it damps the sound. I think thinner strings are easier to play because they are looser, but they are more suseptable to finger gook and pitting/breaking than thicker ones, which hold thier tone longer.