Personally, I like foam skulls. They're cheap, lightweight and it doesn't take a whole lot of work to get them looking halfway decent for your haunt.
I often wipe a litlle woodstain onto exposed areas of the skull to take the "whiteness" off.
just a quick wipe on and wipe off is all it needs.
You may find that the woodstain pits the surface of the foam a little, but to me this just adds extra texture.