The most effective way to stop quickly on a motorcycle is to:

Using both brakes simultaneously while riding in a straight line is recognized as the most effective method for stopping quickly on a motorcycle. This technique ensures that you can maximize braking power by utilizing both the front and rear brakes. The front brake provides most of the stopping force, as it bears a larger share of the motorcycle's weight during braking, while the rear brake helps stabilize the motorcycle and prevents the front wheel from locking up.

Using both brakes together allows for a balanced and controlled stop, reducing the risk of skidding or losing control. It also helps to distribute the braking force more evenly, which can prevent excessive wear on any single brake component and increase the overall safety of the stopping maneuver.

For context, relying solely on the front brake can lead to a loss of control if too much force is applied, potentially causing the motorcycle to tip over. Using only the rear brake is less effective as it lacks the stopping power needed for a quick halt and may lead to longer stopping distances. The engine brake can be used as a supplemental technique to help slow down, but it is not quick enough to serve as the primary method for stopping swiftly. Thus, using both brakes is the most well-rounded and safest choice in a quick stop situation.