Stairstepping, affectionately called the jaggies, is an artifact of a weak anti-aliasing filter. It is not a result of the converter.
The reason why one converter or another may have different performance with respect to jaggies is if there are differing degrees of capture sharpening hidden in the the defaults or in the applied Picture Styles, which to not always report the sharpening they add to the conversion.
Strict attention to jaggies is one way of checking the converter default settings.
