Sue, do you mean simply for piecing or doing fancy quliting over the quilt?

For piecing, I use either 100% cotton, polyester, cotton wrapped poly, or anything I have but I do make sure it is a good quality brand thread. Avoid the temptation to pick up the discounted bargain spools at the dollar store.

It was thougth of at one time when 100% cotton fabrics became popular, that you should use cotton thread as the poly thread is too strong and will eventually start wearing out the cotton weave in the fabric after many years of use. This, I believe was only a theory and has yet to be proven as our cotton quilts just aren't old enough to see any of this usage.

Personally I use cotton thread but do believe that when kids start tugging on quilts, the cotton threadused for piecing will give way long before the fabric thread start breaking.