I've been using 1300m spools of Gutermann thread. It works out much cheaper if you buy the really big spools. I hadn't seen the Aurifil in the large spools but I'm going to look into it because it is a really nice thread to work with.

I always use 100% cotton to piece and quilt although I have many other threads hanging around the house from dressmaking and curtain making so I have to make sure not to grab the wrong one.

It's probably the hand-quilting thread that is clogging up the machine. It's coated to prevent knots when you're hand stitching which causes problems in your machine's guts