Total calories different between Apple Watch and Fitbit Zip

I had used a Fitbit Zip for a while, but just recently got the Apple Watch Series 2. I switched MyFitnessPal data over to the Apple Watch on Wednesday, although I have been wearing it since Saturday. The Apple Watch calculation for total calories is always under the Fitbit projection with difference of 139 to 257:(. Anyone have any idea of which one might be more accurate? I am short, so when I am trying to lose weight, every little bit that I can eat helps. Hate to give up that food:).