Well I personally start all my horses in a rope halter...they are taught to respond to light pressure from the ground up though, so they understand the concepts before I even get on. They are then transferred to a snaffle bit later on, and finally a curb somewhere down the line; however, because of the prior training, I will feel comfortable riding them in a halter. A horse shouldn't "need" a heavy bit in his mouth in order to respond, especially if you're riding with your body and not just your hands.
However, that said, for the average owner especially a green rider, a bit may offer a little bit better control. However, this does not mean that a green rider should ever be paired with a green horse, regardless of the 'means of control'.
"The ideal horseman has the courage of a lion, the patience of a saint, and the hands of a woman..."