For easy to use junglers:

All their kits are pretty straight forward, can do some damage (or alot depending how you build) and stay tanky during the whole game, theres no gimiks to their abilities, their pretty straight forward.
For more advanced junglers who require some practice:
Are all strong picks, most of these have a gap closer, or can attack/ult outside ward range and keep pressure, Having a "good" panth n noc on the team, always makes the enemy team scared to push.
And for some harder junglers, but who can hard carry, these are great:
You need alot of practice, and the runes, to play these guys effectively, All have hard carry potential, and able to delete targets such as mids, supports, (mage ones), and adcs, not to mention all of them can apply early game pressure.
For ez mode:
Its hard NOT to jungle with these guys, once you know how to play them, and your not an idiot, you can nearly win team fights alone, their all tanky, with great abilities and gimmicks that turn fights around REAL quick. These are the champs that you want on your team.