Should I get a Australian Shepherd or a German Shepherd?

I would really like to get either one of these dogs. I am an outdoorsy girl and run and hike a lot and would like a running partner. I just cant decide which is right for me. Size isnt an issue as much as behavior and protectiveness. I want to feel safe but I dont want a "crazy" dog ching after every person that comes near me. Any points, info, stories, advice would be greatly appreciated. The dog will not be alone a lot during the day and will get pleanty of exercise. It also will be both inside and outside thanks