Need advice: 318 or 340 for a 68 Dart?

Yes I have a choice of 318 or 340 at my disposal right now. No 360 in this group. I'm leaning towards the 318 in case I'm in a generous mood and eventually give the car to my daughter who has a leadfoot. Maybe less damage potential with less power. But I see the arguments for the 340 as well so I'm stuck. I'm not going to be doing anything more serious than freeway driving. Yes I want a nice throaty muffler. I don't intend to "beef up" the motor in any way it's going to be left stock whichever option I go with... Thanks for your opinions it's good to have other POV's!