Threads you prefer

I am quite partial to DMC cotton floss, but I had to realize that in certain sashiko uses, the threds are prone to felting and shrinkage, which bunches up the fabric.

On the other hand, I like buying "grandma's embroidery stuff" off Kleinanzeigen. These collections netted me a lot of extraordinarily nice colors and qualities, in some cases a hundred years old.

What do you prefer to use?