I tend to go with the Garmin for accuracy, but I’m still puzzled by the discrepancy. For instance, today I ran either 14.02 miles or 14.69 miles. A 9:30 pace or a 9:15 pace.
I mapped out my run ahead of time using mapmyrun. Presumably it would have accurate road measurements. I guess I understand when it might ping off the satellite funny during a workout, whether it’s weather related or a bird flies by or trees get in the way. But when it’s using a map, I don’t get why it would be off. According to my initial course and the final mapmyrun readout, I hit 14 miles at the same place. I did five loops around a lake, and I’m guessing it measured it the same distance each loop.
I know this is a common problem between devices and that the majority of people go with the less favorable Garmin measurements. I just wish I ran faster, I guess.