Looking at all the abilities and sub abilities of the different bending arts I believe that Waterbending is the most powerful form of bending.
Not only can you alter the form of the water from steam to ice you can also use waterbending to heal. And not to mention Bloodbending which allows you to either freeze or boil someone alive, I know it is very bleak view of the world of Avatar the Last Airbender but it could happen. What do you guys think??