One other point:
The "rules" for choosing a good fabric are the same for both the S&W and the OBW.
If you don't have enough contrast - in value, color, shapes and textures, the quilt will be a dud using either setting.
Although you might be able to get away with a bit more in a S&W because the contrasting fabric will at least stand out to provide some visual interest. In a OBW, a bad choice will just look like mush.
I recently dug up my first (and only) unfinished S&W from 10 years ago the other day. Hadn't seen it in almost as long. I think I might take the top apart and turn it into a OBW.