What size dick does a woman prefer?

Like a man's preference for breast size, it is entirely up to the preference of the woman.

Like a breast, size does not really matter from a performance standpoint.

I agree fully with the answer above, but it leaves the question what do woman prefer. The relationship with their partner is very important to a woman. If she could control the size, woman would prefer a larger girth then length. We are not talking the size of some porn king, but somewhere in the range of 6 to 7" in girth. With a length probably in the 6 to 7" range also.