The anwsers you will get will probably differ as each of us has our own preference regarding this. I personally like and own several 3-9 power scopes but honestly I prefer a 2.5-10 power scope. Where I hunt, it is very thick cover so I leave my scope on 4 power all the time then if I happen to be in a clear cut I can crank it up to 9 or 10 power. I have hunted the open sage brush in Nevada, E. Oregon and E. Calif. the scopes I mentioned above were more then adequate for this type of terain as well.
Good luck,
Slide