I was using cotton thread up until a while ago. I was frustrated with shredding, breaking etc.
I don't know whether it was because the thread changed or my sewing technique changed.
Anyway, I tried Isocord on my last quilt and loved it.
I finished the whole quilt with NO thread breakage. The other thing I really liked is it's thickness. It blends right into the fabric, and a spool/bobbin lasts forever! Less bobbin changes for me is a good thing :)