[Foster]

Seems some brands stretch out quicker than others. I used to use GSP strings all the time, and they were very good at stretching out and holding tune fairly quickly. I often restrung the day of a gig, and while I did have to tune between songs at first, after a few pieces they seemed to settle in pretty well.

But as has been said, nylons are what they are, and more susceptible to temperature, humidity, direct sunlight, etc than are metal strings. It's annoying, but we get used to it.