I have a Tin Lizzie 18LS. The recommendaiton was King Tut on top and So Fine on the bottom, which is what I usually use. I always get a good stitch with that combination. King Tut is cotton, so there is lots of lint with it. I also use Omni thread. It's a poly, so no lint. It works well in my machine also, and is less expensive than King Tut. You can purchase the Omni in 6000 yard cones. King Tut is only 2000 yards (I think), and costs more. These are all Superior threads.
I haven't tried other brands in my machine. I tend to stick with what I know works because nothing is worse than problems with tension, poor stitches, or thread breakage. I have had my setup for less than a year. Perhaps as time goes I'll get braver and try other brands.
Kerry