Jg main here, by far my favorite champ is j4… hes not hard to learn but he has so much versatility that you can learn how to do or play him with or against almost anyone, so the cap for him is near limitless. He's also very strong in the meta and if in competent hands is capable of hard carrying. Watch out for Jax though he's your hard counter on jarvan.
Easy champs to learn jg on that are meta would be Warwick, rammus, zin xhao, yi.
To a new jungle the best advice I could give you is to play some games on those easy camps so you can get the basics down, read jungle guides on the farm routes and builds for each champ. Then once you get a decent understanding switch over to a jungle that scales high with skill such as rek'sai, Lee sin, jarvan. They are so versatile as jungles that you can practically play them with or against any team, with enough experience they will let you really shine as a jungle. It will take more games to do decent with them but if you persevere it will be much more rewarding. I played easy champs for quite a long time and wondered why I couldn't advance or carry reliably, once I started to main jarv and rek I realized what I was missing. I wish I'd played more Lee sin. A good Lee sin is horrible to jungle against