I would also consider the use of the item you are making. I find the poly quilting thread I use holds up very well through use and washing. Some of the threads I use for wall hangings, I choose because they have a nice sheen and look good. But some of them are not as strong and I don't need them to be as I am not washing my wall hangings frequently and there is little wear and tear on them. Serger thread varies in quality. Some is not very strong; some is very strong. The manufacturer's website usually has recommended usage for each of their threads. I used a 40-weight cotton thread in one of my quilts, and the stitches started to break after a few washings. I learned later that this particular brand was made of poor-quality short length cotton. After all the work I put into my quilts, I will not save a few dollars on buying poorer quality thread.