The key is the pressure. The bare hand is just as good as anything else. The problem is that you will probably want your hand back at some time or another. In my early days on an ambulance (before the EMT existed) I often used my hand directly. It is lots better to use something else, mostly because as the bleeding slows you can wrap the gauze, towel, etc. without removing the pressure. Most of the time we used gauze pads or kotex and Ace wraps. Hold the pad while you apply the Ace. The big advantage of combat wraps (before clotting agents) was that you could apply pressure without keeping your hand in place (you might want it for other reasons).

The sterile pad is also good because it doesn't add anything undesireable to the wound.

Respectfully,

Jerry