The old myth has been around for years, claiming that some calibers are "brush busters". As others have said, all bullets will be deflected by brush. You may still get lucky and get a clean, killing shot, but you should have enough respect for the animal to not depend on luck. Wait for the clear shot. That said, of the calibers you mentioned: The .270Win is a proven deer cartridge but limits you to lighter bullets. The 7mmRemMag is a very flat shooting game getter capable of taking all game up to the ones that will eat you! The 30-06 is the best all around of the ones that you named, capable of taking any game in N.America.