My wife says the chief advantage of a big cock is psychological, knowing that she's getting stretched out by a leviathan pleasure rod. Just the visual gets her wet. In terms of physical pleasure, thickness matters most, because of the "full" feeling it gives her, something she never felt with ordinary or undersized boyfriends.
But for long-term companionship, she just wants a reliable guy who will pay the bills and wash the dishes. That's where I come in!