It's not that simple. Some women like it fast, some women like it slow.

Many women like it slow at first, then building to faster. Note that faster does not equal HARDER!!! The top of the vagina is capped by the cervix, which from my own experience is a very sensitive ring of muscle. Hitting it with your penis feels akin to punching an already bruised wound.

Some women like slow, full strokes. Other women like fast, shallow strokes.

So it is impossible to answer "do women like it fast or slow" because you cannot pick just one.

it all depends on person's biorhythms. You have to work it out with every girl individually.