A Little Confused

On my treadmill, it says that at a speed of 2.0, I walked a distance of 2.003 and burned off 246 calories.

On my Nike+iPod app (with the sensor in my shoe), it says I walked a distance of 4.28 kilometers (2.65 miles) and burned off 500 calories.

On Myfitnesspal, it says that by walking at a speed of 2.0 (slow pace), I burned a total of 286 calories.

Which one do I go by? I am just a little confused. Is the Nike app like this because it's considered a running app (I thought it could be used for running and walking, but I maybe wrong). Either way, I am proud of what I have achieved. If any of you have insight into this, please let me know :-)