shaco or jarvan?

What sounds more appealing to you: Being extremely manly and shouting Demacia while dealing Tons of Damage(tm) with just a little AD itemization , or shitting on whichever enemy champion is unfortunate enough to be your mirror via being a sneaky little bitch ?

As a Shaco main, I will warn you... Only play this champion if being a sneaky/tricky jackass sounds very appealing to you. If you're looking for a reliable jungler with nice ganks and great teamfight, pick J4. If you're looking to have some real fun (you probably won't have much fun or win much your first little while playing Shaco cuz he takes time to learn) pick Shaco.

If you want versatility and stability, Jarvan. He can do a lot of damage, can be pretty tanky, has mobility, has CC and he's good in pick comps as well as team fights. He can be played very effectively Top and Jungle, and as a niche pick he is sometimes played mid (he works much better than you'd expect in mid).

If you want to main a champion that is very hard to play at a high level but that you can really snowball games hard with and give people nightmares, Shaco. But he's hit or miss. If you fall behind as Shaco you become pretty useless. And if you want to be a decent Shaco, you need to main Shaco, he can't just be one of the 20 champions that you regularly play.

Jarvan, he can bring much more overall utility for the team.

Shaco falls off late game HARD unless he's fed all game. He's almost useless in teamfights unless people hit his boxes just before, or he stealths to the enemy's back line and Backstabs the ADC/APC. That said, he's pretty damn strong early game.

J4 is mostly used for his epic chasing potential and his ult. I gotta say, his ult is both really goddamn annoying and a godsend. AoE spells immediately after wreck entire teams. He still manages to do a lot of damage, even if he builds tank items. J4 ganks are glorious.

Shaco takes a different mindset than most every champion in the game as well as a lot of practice in order to figure out what you are capable of.

I'd say Jarvan unless you really feel strongly about playing Shaco.

J4 is definitely easier to learn and his skills compensate a team well. That being said, be sure to cancel your ult when you need to. J4 is good and has huge potential, but doing well with him doesn't guarantee a win. It may be me but with different accounts for the past 2 seasons it has been hard for me to get a win rate above 50% with him. My KDA is decent (~6/3/9), but sometimes it's hard to win late game.

Shaco can be very annoying to the opposing team, especially his boxes. He is harder to master and he really requires other teammates to go tanky (not a necessity but it helps).

Note: J4 has one of the best gap closers in the game (flash+e+q+ult, takes you across half the map).

If I was told correctly, Shaco is a jungler that doesn't need a Leash, so that might appeal to you. I personally avoid the jungle role like the plague though.