It depends on your target distances, but considering a standard 100 yard range, these are my suggestions:
.223
Here you generally want a higher magnification scope so that, in part, you can see the small bullet holes. A 4x-12x is fine, and scopes up to 20x are really not out of place.
.30-06
Kinda hard to have such a gun for just target shooting. For most hunting applications, a standard 3x-9x is ideal, and you can use this for "target" shooting too.
.45-70
You really don't need anything over 9x. In fact, 9x should be considered high for such a gun. I would look into a 2x-7x or even something like my Elite 3200 in 1.4x-4.5x.
Zachary