Who is the easiest Jungler

I'm going to say ... incredibly safe, brainlessly simple, overpowered and effective.

He's the Iori Yagami of League of Legends.

One button to sustain and kill jungle mobs. Press this other button from fog of war to blink through the wall and surprise your opponents. Press the other two buttons so your opponents cannot fight back.

To just be in the jungle? Warwick. To actually gank and stuff? I would say someone like amumu or rammus

Clearing is easy IMO. If you get counter jungled, you can use your e to dodge all basic attacks and stun the enemy, which can help when getting away, killing the enemy, and can help in ganks. Also, once you get your ultimate and get a sated devourer, you become very powerful.