Well, if it had to be on morale terms, Id say its on account whos life is taken. If its older for a younger, it might make more sense. Then there is conditions on whether that person is, say, a parent or someone important and essential for something else. Its all details, really.
the strongest point in this is what renegade and i have said before. Where one of these has guarenteed life, the other does not. You also know what to expect of this other persons life and not of the unborn child. The unborn child has a higher level of capability to have birth defects or simply not make it. Also, in order to win the argument your going to have to find a way to call an embryo an incapable human being, such as my example with the spouse in the hospital. Without a living will, if he is incapable of saying what he wants done its up to the spouse and/or the parents. In this case the embryo has no say in what happens to it, therefore it is the mother and fathers choice, since it has no spouse. In the end its not truly a question of morality, its a question of "would you like guarenteed life with small difficulties, or would you like the possibility of no life or massive difficulties.