I have heard that CorelDraw is the best, but has a price !
Free, I tried 2 programs: Wintopo and img2cad.
Both returns dxf files opened in AutoCad, entities not smooth and a awful text!
See inkscape (it's free)
I have had the best success rate with Print2CAD. It does cost, but it has multiple settings to tweak the conversion and can "learn" for future conversions.
tray vextractor or autocad raster design
Inkscape is the best. You can see my tutorial here: https://grabcad.com/questions/how-to-convert-jpg-to-prt-or-step