Who cares which is correct? If they are consistent in their reporting, then you'll know which route has more climbing and descending in it.

I wouldn't expect two different devices to report elevation gain loss the same way. If we really got to talking about it I doubt that even we would agree what constitutes elevation gain or loss.

If I'm on a fairly level road that goes up and down a foot 20 times over the course of a mile do I count that as 20 feet of gain/loss? What if it's 5 feet 20 times in one mile?