I own a Pfaff 788 which is a total mechanical serger. I wouldn't trade it for anything because it is a workhorse (purchased in 1992). But, if I wanted to serge much more than 2/3/4 thread anything I would need a new one. The threading isn't horrible but there are now models that are much easier to work with and mine does not do a chain stitch.
My advice is to take sample fabric on anything you think you might want to ever sew, use a different color thread in every looper and needle (much easier to see exactly how well the machine actually stitches), and test drive everything you can get your hands on in your price range (new and used). Compare, check the warranties, dealer support, etc.