Comparing internal failure rates is a good thing to do, but make sure you're comparing apples to apples. Cochlear considers an implant to have failed only if they can find the problem after it has been removed. AB considers an implant to have failed if it has been removed.
I had a group of electrical engineers review the technical specs of the devices, and they thought the AB implant system was easily the more advanced of the two. They were particularly impressed with the multiple current sources for the electrodes as opposed to one current source for cochlear.