A few years ago I happen to see one of the first zigzaggers Bernina made in the late 1930s. It is heavy cast iron, they came in black or green. They only do straight stitch and zigzag, and I think they are general low shanks. This is sort of the ultimate machine for me; a very smooth running, solid work horse. I don't really need much more, and if I need a stretchy sitich on a jersey hem, an additional serger could be a good solution. However the case, I would not mind a brand new latest model Bernina either, they cost a lot though.
I can't really decide on just one model, but for the moment I am working on an old Elna Supermatic, it is pretty close to ideal. It has a cam stack which takes lots of different disks, rather advanced for a 1950s model, with double cams and stitch patterns with reverse stitch combination; it does rather nice simple over lock stitches and stretchy seams. Mine is still a bit noisy, I hope to improve on when I get a few wear parts replaced (rubber pulley and a bobbin tire). I might have to take a look at the motor too.