The last Bernina that I bought I was told to not use Coats and Clark threads, that I should use Guttermann or the other brand which I can't remember the name now. I have noticed that since I have been using these threads that there isn't as much lint that forms in the bobbin/dogfeed area.
I also just learned that certain threads are put on the spool differently. That determines which way you put it on your machine vertical or horizontal.