This is a question I can not answer exactly completely, as I can track only deaths resulting in a kill credit for another player. So most of the puffy ack deaths (over the strats for example), or someone dying to field auto-ack won't show in the records.
That being said, in the first 4 months of 2013 gun ship/field (manned ack) has been credited with 8.3% of all plane kills, AA vehicles & PT boat with 9%. (Other GV with 4.8%).
From my experience in AH, I would estimate the number puffy ack deaths to be considerably lower than the number of deaths by either manned ack or AA vehicles.