Look for an older all metal geared machine with multiple stitching options. Forward and reverse stitching along with straight, zig-zag and the ability to do a bar tack are all beneficial options. A free arm machine helps a lot with smaller circular pieces of work.
Some brand names I have heard about are Necchi, Pfaff and Singer.
FWIW I have made quite a lot of my own gear with a Singer home style sewing machine. It is a model number 538 Stylist.
If you purchase and older machine get it checked out thoroughly and ask the owner if you can run it through a test by sewing something simple and quick. A lot of times machines that do not appear to function only need a good cleaning and lubrication to sew like new.
Having a good local repair shop close by is an added plus.
By all means try to locate a manual for your machine. It will help you sort out small problems like adjusting thread and bobbin tension for example.
I hope this helps.
Newton