Well, after consulting with my wife here is our decision.
We'd pick an early iron machine with zig-zag that uses a common needle such as the 15x1, and bobbins such as the Class 15 or 66, and common low shank feet.
ZZ machines are very useful for making clothing, patching, edging and that kind of thing.
We don't necessarily need decorative stitching but one with that capability wouldn't be excluded.
Right now we have several very good candidates for such a scenario. None of them antique, a couple are barely classics.
Joe