Calories burned: MFP or MapMyRide

In the past, I'd been measuring the distance I rode, then calculating the average speed and entering it in MFP by selecting (for example) "cycling 12-14 mph" and entering the time. Today I actually tracked my ride in real time using the MapMyRide app for my iPhone and it gave me a total of 789 calories burned. When I went to log that in MFP, the MFP app (using the "cycling 12-14 mph for 53 minutes) calculated 688. So, which is more accurate? I'm tempted to say MapMyRide (not just because it burns an extra 100 calories!) but because it uses GPS, calculates elevation and measures speed rather than using a generic range. But is that right? Anyone know?

Thanks!
Bryan