I don't think I've ever used the same thread in the bobbin as the top. I always use bobbin thread for the bobbin when piecing in the color of my backing. I use all brands of thin thread. My very favorite is silk thread for bobbin and top for machine quilting. The thread is super strong and seems to melt into the fabric. It's expensive but I watch for sales and have a good collection of the YLI mini cones. Superior now has silk thread and it's very good Invisifil and Glide are the next two favorites. Aurifil bobbin thread is very good for top and bottom. C&C has a super fine bobbin thread on a mini spool it's size #80. I experiment with all types of threads. I like Connecting Threads Pro threads when I want the stitches to stand out, it's strong and doesn't break at high speed. My stash of threads is about the same as my stash of fabrics. I have to have both.