Which is a Better Workout, 50 Minutes of Spinning or a 4 Mile Run? [POLL]

A lot of fitness buffs are always talking about what a great cardio workout is and everyone and there dog is always talking about the best way to loose weight. If you have ever taken a spinning class you know that is no cake walk. If you take the class seriously you won't be able to move very well the next day due to sore muscles. Because I have been trying t get into good shape for a couple years now I truly do wonder which is better...50 minutes of spinning or a 4 mile run?