Either kind of call can and does work in the right situations. It has been my experience that calling is best done when they are a good distance off or they cannot see where the call "should" be coming from. What I mean is they should be far enough off to not be able to notice that the call is coming from above (if you are treestand hunting), and there should be enough cover so they can't just look over and see that there is no grunting buck or bleating doe. That way they are more inclined to come check it out. I only use calls as a last option though.