I currently have 4800 IP, and i really need to find another jungler to play. I currently have zac, olaf, nidalee, rumble and amumu, and i'm looking at champs such as Jarvan IV, HEcarim or Graves. Can you please help with my choice with maybe a list of pros/cons for each, and their playstyles? thanks
Depends on your playstyle. There's different jungler types and you have some of each. I've played to Level 7 Hec & Graves on my main and 5s on alt here.
Hecarim has a weak early game first clear and doesnt get strong until triforce, at which he's still squishy until he gets the first tank item of cinderhulk, deadmans or visage so up until this point he's vulnerable to invades and cant duel well but has very strong ganks. If you laners aren't getting ass pounded and has some sort of CC, you can setup ganks very well in lanes with them. If theyre crap and crying about not getting ganks while feeding, then you wont have a huge impact since getting ganks in is a huge source of income to pay for that expensive triforce. With jungle buffs it's harder to rush triforce after talisman, so you need to get the tier 2 jungle item (skirmisher's sabre or stalker's blade) to stay healthy. Hunter's pot as well too if you frequently give blue buff over. This delays your triforce power spike and tankiness further so how well you do really relies on how fed you can get from ganking. Once you get to mid-late with him, hes a total monster and huge asset in teamfights being able to dive or peel. He's useful in any comp.
Graves is more of a power farmer. Provides no CC during ganks and relies on a front line and CC/peel for him to do well in teamfights. Able to full clear the jungle while staying very healthy and have incredibly strong invades. He's better played as a counter jungler to invade their camps or take out their jungle, or to finish off weak lane opponents rather than a hard ganker. If you lanes aren't winning or staying even at their 1v1 it's hard to gank for them. You'd spend more time clearing camps and clearing enemy camps to set them behind while trying to hunt the other enemy jungler since your Q will do tons of damage with all the walls in the jungle and dash can let you hop walls to get take more unusual paths they dont expect. He's also super strong at taking towers. If the enemy laner leaves, you and your allied laner can take their tower pretty quick
I only use J4 in 3s. My go to picks in 5s is Hec, Vi and Graves in that order with a rare side of Xin
I find J4's clear speed in SR a bit too slow since he relies a lot on autos and only 2 offensive abilities. His build is a bit contradictory too since he wants to be a tank in teamfights, but also wants items like 
to brawl with damage, have strong dueling power and to kill people. If you have a good team you can go hard tank and just rely on his passive to do the damage, but IMO his big weakness is needing to use 2 abilities to get the dash in to dive or peel, and after using those 2, your damage output is severely gimped.
Using all your non ult damage abilities for the dash also leaves you super vulnerable where Hec can Q or R in then use the other to get out if things go bad, and Vi's Q dash is a short CD to get out. J4 can't get in and out (E CD is too long), he goes in and either they all die or you die
Your ult can screw over your own team too if you trap allies in, or if it shoves allies out who could be doing damage but zoned by the crater and you're left to decide do I let my ally in to do more damage at the risk of the enemies I ulted to escape? At the same time, so many champs have a dash now that they can get out of the crater so his ult really just becomes a damage nuke
Pretty clunky to use and kit is restrictive. I like him in 3s because tanky damage champs especially with CC rules TT.
