I cannot emphisise how important good thread is. I have used Coates and Clarke (on my first quilt), and it works OK. I have heard that it doesn't hold up over the long run and that friends don't let friends use Coates and Clarke. So I have been using Mettier Silky finish thread for awhile. Works great. My Bernina just doesn't have tension problems no matter what thread I put in it. Do a slight (and I do mean slight) adjustment to the tension control and it handles anything from 50/3 to 40/2, even some thicker stuff in the bobbin.
But... I used some cheaper stuff (I don't remember where I got it) in my Elna. All of a sudden it started skipping threads, creating huge messes on the back side of the fabric. What the heck? Turns out the cheap thread was leaving deposits of fiber on the hook assembly of the bobbin. Cleaned it out, put in good thread and the skipping went away. Like that.
Check it out on yer Brother. Most people who have those machines like them.
If it's hopeless, I can always recommend a Bernina 830. About 400 bucks in full running tuned up condition. And it will last you forever.
tim in san jose