If you get scratches with a blade, then you will get scratches with a leather, a cloth, or whatever you use, as you haven't rinsed all the grit etc from the surface of the car.
Make sure you wipe the blade after each stroke, with a m/f cloth or similar that you can then throw in the washing machine ready for next time.
The scratches might also have some from a sponge, if you insist on using them, as they WILL trap the grit and then scratch the car.