My favorite has always been Bodymedia. It has more sensors on the device then any other fitness tracker. The downside is that you wear it on your upper arm.
I recently upgraded to the Samsung Gear fit. Which IMO is not a true fitness tracker. The accuracy is horrid. I'm hoping Samsung will make improvements. It's just a pretty smart watch atm.
I'm anxiously waiting for the Amiigo or Bodymedia Core 2.