jungle is amazing if you like being a utility based champion focused on catching people out AND dueling while simultaneously tanking for your team and saving lives across the rift. Shen has a great kit when used properly and his clear is god-like after his first back (when you get a bit of health.) I recently hit rank 7 on Shen and I can say he's one of my best junglers.
is a bit of different story, being a pure glass cannon while having tons of kill intentional. Evelynn taught me how to counter jungle and now (Seriously) in about 80% of the games I play as her, I pick up first blood and set their jungler back all game. Ignite + Smite and ambush at their first camp, if they are there then ignite them and go ham with thunderlords, if they aren't there then take that camp and leave the small mobs so the camp doesn't respawn until they clear it.
The titan of the jungle, Nautilus destroys the monsters in the jungle at every level with his amazing clear, and his ganks are terrifying and effective. Nautilus was one of the first junglers I had and honestly I think he's secretly OP in the jungle, haha. He's that good, every gank is a guaranteed flash or kill if you play it right.