I darn on my Singer 201 treadle using the normal standard foot. I haven't quilted on this machine since I use my fancy Bernina 440QE when quilting. However, I know the treadle would do a fine job. The stitches are perfect. I loosen the tension on the pressure bar until my fabric moves freely under the foot. I don't even drop the feed dogs. When I patch my husband's jeans I can go between several seam layers of denim to a single layer and there is not even a hiccup.
I also use the 201 treadle to do free motion embroidery. When embroidering, I use the technique suggested in the manual; remove the foot altogether and place my fabric
tautly in an embroidery hoop. The work is wonderful, it is hard to tell the right from wrong side just by looking at the stitches. Those old machine are marvelous!
To answer your question, I think the darning/embroidery foot might give a better view since it wouldn't obstruct as much of the fabric. But, I don't even know if that foot would work with my old Singer 66's and 201's; I haven't tried it.