Comitting adultery, though this is a bad choice. It's like saying decide whether hacking someone to death is worse than bludgeoning them to death.
I agree this is a bad choice. One is direct violence, the other is an a more indirect type of pain.
I don't think rape can happen in a marriage that is anywhere near healthy. A husband and wife try to accomodate each other's needs. If they're not in the mood at the same time, they'll compromise. A man or woman may sometimes "perform" when they'd really rather not, but by the same token, a partner who really wants it will sometimes forego sex if the other partner is clearly not in the mood.
Bringing charges of rape within a marriage should only be done in the most extreme circumstances, and if that were ever to happen, it really couldn't be said that a marriage actually exists.