Depends on your stance mostly. If you have your right hand semi ****ed, then release it like a whip half way, you have a better chance of surprising your opponent.
If you have your right hand right near your chin, like a normal boxing stance, won't be as fast, and sudden.
Most counter punchers have their hands away from their body like an Ali, Roy Jones. It's much easier to counter that way, and your punch comes off quicker.
If you stand in a defensive stance, your punches are more predictable.