I had my SC for about 2 yrs and the damn circular flare issue always annoyed me, even though it was pretty much predictable and didn't show up often. I traded it for a Kowa Six kit with some lenses, but after not adapting well to the camera (and it had an annoying focus shift I didn't want to spend to fix) it came back to me. After trying other 35mm lenses (even an MC) and looking back at photos I did with the lens, I decided to give it a second chance, it's now everyday in my bag mounted on a Hexar RF. it's quite a versatile combo (i shoot 800 iso color film).
The speed, size and price are really hard to beat.
vs the MC, I felt almost no difference, really, the MC tones felt a bit more contrasty but the difference was very, very subtle. same round flare.
vs the 1.7 Ultron, it's considerably shorter and a tad faster, also it gets backgrounds a bit more blurred. the bokeh on the Ultron is more neutral, won't bring as much attention to itself. light balls on the Ultron won't have much brighter edges as the Nokton's. incredibly resistant to flare, even without the hood (never got any flare with it, actually).
vs the 1.2, it is much, much, much more discrete on the street, smaller, lighter and easy to carry (sometimes i split lens and body and have them on coat pockets so i can take the camera somewhere with no bag at all). the 1.2 bokeh is much, much smoother and neutral than the 1.4's. light balls sometimes are incomplete (like a crescent moon, missing a corner), which is not a complaint, i like it, but the bullseye rings in them kind of annoy me a bit in certain situations. the 1.2 feels more robust, but still I like the 1.4's smoothness in both focus and aperture rings, never shot at a wrong aperture due to its smoothness. the 1.2 is very resistant to flare, and i shoot without the hood always.
vs the v4 summicron, it's just a bit heavier but the size is pretty much the same. I've found the v4 to get a purple polygonal line flare in certain angles against the sun without the hood (of course, that's what they're for!), which sometimes can be annoying, but nowadays I only use it with the square hood and didn't have many flare issues. but that made me see the round flare with different eyes also, as it won't compromise images as much as this polygonal kind of flare.
i've bought an f2 canon 35mm also, but haven't received it yet from a friend, I'll post my impressions afterwards.