You have to break in the strings. You’re also like to hear a slight rattle till they completely break in.
This is true when you get a new ukulele as well as when you change your strings. You tune and play, they stretch, you tune again, they stretch, you tune again, they stretch and so on.. I think the first day i played my new ukulele i repeated this tune, play, re-tune cycle around 10 times the first day (1-3 hrs of playing). It’ll keep slipping out of tune for a few days..
Eventually the strings start staying in-tune longer.
I played a couple of YouTube videos on laptop speaker and couldn’t tell any difference between any of the string sets played. Then i put my headphones on and played the videos again. This time, i could tell the difference.
The ones i liked were D’addario Nylgut, Freemont Blackline, Aquila Lava
Long story sort, low-g for melodies, high-g for strumming