You´re ALL wrong !!! [:@]
This is the best sponge!!!

[:D][:D]
Jokes appart, the best sponge I´ve worked with is the sponge from my airbrush package

Yes, the blue one. In general, all the sponges employed for package are right, as they are very fine. I´ve tried sponges typical for having a pleasant bath and they do not work properly.
I cut it with my modelling knife in order to get the desired shape as sometime we need chipping in very specific places, some times, hard to reach.
If you´re using acrylic paints, or even enamel, the procedure is always the same.
1.- Study the palce where you want to add some chipping
2.- Cut with a cutter your sponge according step 1.
3.- Take it with your tweezers (I never use my fingers as I use to cut the sponge in little chuncks usually with just 5-10 mm as the maximum dimension)
4.- Soak the sponge in the paint (sometimes, I add some water to the Vallejo paints in order to get the desired effect, that is not always the same)
5.- On a tissue paper or similar, download the paint until it almost does not remain in the sponge.
6.- Apply the sponge on the desired surface. Do the chipping in several times, do not try to get the final result just at the firs time. repeat the procces.
Anyway, in my humble opinion, best results are achieved using the sponge AND the brush, not only the sponge (or the brush). Scratchs always with brush, polished surfaces (with bare metal), with sponge, for example. Try to mix this effects to get the best result.