My tension is usually automatically set to 2.8 (for embroidery), but I often have to reduce this to 0 (or what my machine calls 0) in order to stop the bobbin thread from showing on top. I think you have to treat the stated tension as a relative thing rather than a definite number.
My machine likes Gutermann thread, but if it's variegated it reserves the right to throw it up. Madeira, too is usually great, but occasionally it takes a dislike to a specific reel. Metallics of either brand are better with a topstitch needle than a metallic one for some reason. It hates Sim threads, which is a shame because I have a lot of them. I sometimes try to sneak one in, but I never get away with it.