I hate vectoring for web jpg images. It's always choppy. What I do it put it in photoshop and raise the dpi about 25% at a time until I get it up to a high dpi (like 400+ dpi)
and then I can sharpen or even smooth and fix by hand. But once I am at a good resolution, at least I am not wasting my time. Fixing up a 72dpi image is getting you nothing,
But fixing up a 400 or 600 dpi image, at least it is useful after you make the effort.