Assuming were using FMA type alchemy, and since we don't have any specific matchups,??I'd say go with alchemy.
1. Ed was able to turn a villian's body into ethanol. Even assuming that he could only do it becuase the character was watery, he'd still be able to evaporate a waterbender's water source. (If we can use the manga too, Mustang can seperate water into hydrogen and oxygen. And then ignite the H into a giant explosion.)
2. Alchemists have been able to control water, fire, earth, air and metal. There are examples of multiple elements being used by one alchemist. They can create most if not all of the effects caused by bending.
3. Alchemy is capable of things bending isn't. Surrond the bender with an army of armour suits that each contain a bit of your soul. Turn the bender's body into a bomb. Make pink sparkly things surrond you and freak out the bender.??Or just break down a bender's body.