I think the first question you have to ask yourself is what do you want it to do. Do you love the fancy stitches? Do you want a large throat space? Do you want knee lift? Does it need to work on a frame? Make a list of the features that mean the most to you and see if there is a machine that matches them.
I just bought a new Brother 1500s. It is a straight stitch only machine with a 9 inch throat. Throat space was my big requirement because I have a smaller machine that does fancy stitches.