I never understand the arguments about what's more accurate or this device give one thing when another device gives something else. As long as you take your number from the same source, then you'll be able to see the relative differences in your performance from one to the next with reasonable accuracy. Especially if you are looking at the data of multiple rides.
None is going to be what the real number is. Calories in particular as we don't have sensors to measure the things that will more accurately tell us Calories burned. Even power has some guesstimations in it's numbers.