why is the Jawbone Up and Up 24 so different in step counting from the Fitbit Charge

I have worn all three units on the same non dominant wrist at the same time and find my Jawbone units report 25 to 50 percent less steps than the Fitbit. I also had to replace my Fitbit because the band broke. But I had consistent results between the two Fitbit bands. It's just that the Jawbone units are always lower than the Fitbit units. Which is more accurate? Obviously being linked to MFP, the excersize calories are really different. Has anyone else noticed this? What did you do about it?