Earthbending is the strongest bending in Avatar.

First, Earthbending can be concentrated to be able to sense other's presence. It's easily the best for surprise attacks.

Second, Earthbending can basically use the world to its advantage. They can make it to their advantage.

Third, You can use it anywhere. The whole world has ground. So Earthbenders have an unlimited supply of ground.

Note: Also, If you hadn't watched Naruto... then you won't get it really, but It also makes a good point, In the ninja war, Garaa (The sand dude, also, yes, the ground can do Sandbending) uses sand on Madara and Madara tried to move but couldn't, so Earthbenders can stop others movement and force them to move. So to sum it up.

Earthbenders can Bloodbend.

Furthermore, sand is small, so it can go into water and mover water too. Because to back it up, when Garaa stopped him from moving, we got to see up close what happened, the sand was in Madara's blood, so it should have no problem getting into other liquids. To make this all simpler,

Earthbenders can use any liquid they desire to beat anyone.

Earthbenders are technically can be called;

-Poisonbenders

-Diamondbenders

-Stormbenders

-Acidbenders

-Firebenders (They can use coal and iron from the ground)

And more.

Also, Earthbenders can literally dominate anything.

To hold all of this liquid? Use a gourd. Be a rip-off Garaa. lol. But it still gets the job done.

Because first of all, we can easily take out one bending art without a fight;

Firebending. Earth can easily beat it because it can use lava bending, a stronger version. No matter what. Even If some dude in TLOK learns white fire, whoopdy doo. Great job. But Lava bending can easily K.O it.

Waterbending. Technically water bending only decent bending his Bloodbending. But that can only be achieved on the full moon. But let's say it was a full moon. Bloodbending can only be in use when they are seeing the other person. All the Earthbender has to do is create a wall around them, or just create a wall to trap the light out making the water bender rendered useless. Plus, it can just use sand to drain the water up.

Airbending. Airbending is ok... but honestly not the best. The only good thing is the Energybending. Yet, like Bloodbending, but actually more GARBAGE. Energybending needs you to be touched in order to Energybend. So basically, It's garbage. Airbending loses easy.

I literally gave you proof of all of these to back it up. To sum this up.

Firebenders: Use Lavabending.

Waterbenders: Use Sandbending

Airbending: Make a wall and just make him tired and boom.

Done.

Earthbending has the power of Thanos.