What is the preferred method to transport and unconscious victim?

If you are in a situation where you are the only person available, and you need to move the person immediately, you use the drag carry.

Stand behind the person's head, and use their clothing to drag them backward, supporting their head and neck for as little movement as possible.

Remember, this is only in an emergency situation where they must be moved immediately. Doing this can result in severe spinal injury aggravation resulting in paralysis or impaired motor function, so if at all possible you should wait for a second rescuer with equipment, or an ambulance.