Exercise is typically 6-8 calories per minute. More than 8 is achievable with very high intensity or very high impact work. Cycling is neither. Endomodo gives you about 10cpm, which is very high for cycling. Spark says 5.6. This is much more realistic, if a little on what I would assume would be the low side.
I tried googling it and using a few other sites and got:
I think you should trust in the Spark value.