Look for a prospect with absolutely no hoof problems. It should have thick hoof walls, concave soles, large frogs centered directly in the middle pointing to the middle of the toe, with equal hoof development on either side. The horse should not be down at the heel. Be particularly suspicious of any excuses the owner makes for hoof flaws. I have known horse with white, black, and striped feet, some good, some bad.
Black feet tend to be harder, with more of a tendency towards brittleness.
Although white feet may wear down quicker, they may be less likely to crack. But I bet you can find farriers who dispute that. Therefore I prefer horses without white stockings. Since the color of the hoof wall is determined by the presence or absence of color above it, they will, of course, have black feet. For a discussion of equine limbs, read and reread all of Dr. Deb Bennett's articles in the Arabian Horse Express.