My favorite piecing thread is Mettler silk Finish cotton. It is a bit pricey but I have found I usually only need 2 colors. I use a very pale grey for all my light colored piecing and a dark grey for my dark piecing. It was a tip from a lady at my LQS and so far I haven't noticed my stitches showing. For quilting I like Superior Threads King Tut 40 wt.