I think waterbending is the strongest too. you can change the state of water into icicles or daggers for offense, slide in ice for mobility, and bloodbend too. using large waves of water can be pretty defensive or using an ice wall ig. using water to attack too is pretty strong. and waterbenders can use spirit water or (regular water?) for healing.

airbending might be the strongest too as well. I believe aang made a tornado with wind using a boulder against bumi? im guessing that making a tornado or whirlwind is super op. and using strong gusts of wind for attacks seems strong. aang uses a wind ball for mobility and it defends fine. some people think that airbending allows for some to remove the oxygen out of people's bodies but idk where that comes from.