If it was due to needing to cut back, I'd probably keep my big embroidery combo machine - because I can do everything on it, including FMQ.
Now, if it were for "worse case" situation, I think it would be the Singer 401G. This is like the Singer 401, but is the model that comes treadle ready. That way I'd have a treadle, but it would be a swing needle machine that takes cams for lots of decorative stitches. It also takes "modern" bobbins and needles so no hunting for vintage stock to use it.
It's hard to think about only having one, right now I'm working on downsizing to under 100