Have you sewed on both machines? I would buy the machine that does the best job on a straight stitch seam and that I enjoy the most. Machines last a long time, and a machine I really enjoy using delivers more hour-by-hour pleasure than other machines that might have more features or not do quite as good a job for me. If sewing on a vintage machine gives you a lot of pleasure and the stitching line is good, choose the featherweight. If the Janome is more fun for you, choose that one.
I can't see vibration during transport as being an issue to consider unless perhaps the machine will be strapped to the back of a motorcycle or you will be driving over cobblestones a lot. I think that brings the decision-making into the realm of over-analysis (or analysis paralysis).