Fitbit or MFP data

OK, so this is perhaps a little pedantic, but I have been using the myfitnesspal database to find exercise/calorie burn and enter the data into the myftnesspal app, which I have associated with my fitbit tracker. All this works fine, however I want to know why there is such a disparity between the apps that relate to the types of activity and calories burned. For example, I go to the gym, I do a vigorous half hour on stationary bike and myfitnesspal suggest I burnt 607calories whereas if I enter the log from fitbit calories burnt suggests 469 calories, the Matrix bike in the gym suggests around 250 calories. Or a 1 hour spinning class on MFP = 811 Calories whereas on Fitbit = 581 Calories...

Which would other users recommend? I have feeling that MFP is incorrect and sets Calorie burn too high, I cannot find the details of how they arrive at the calculations for each form of exercise, anywhere, I know, for example that calorie burn is also based on an individuals biometrics, so please help fellow fitbit users, am I better using the Fitbit data OR MFP for logging exercise?

I am getting a Wahoo HR monitor that should be the most accurate, for tracking exercise, but it is certainly an issue worth exploring until then..

Of course MFP suggests using its datasets, however if they are too high, then??

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