For sheer balance?, the junglers who have both extremely powerful ganks and snowball potential, dueling potential and then lategame teamfight defining potential.

They invalidate the junglers that do only a few of these things "Yeah,
has great early ganks, clear and duels, but he sucks at lategame. why not just pick
?" "Yeah,
has unexpectedly strong duels, great clear, and some awesome lategame teamfighting, but his ganks absolutely suck, why not just go
?" "I know
has fantastic ganks, great lategame initiation and such, but his clears suck and he can't duel for shit, why not go
?"
HOWEVER, since the champions that are good at everything happen to be great at ganking, this invalidates not only a large group of junglers, but a large group of LANERS:
-
-
-
-
-
Would be very viable, but their very nature of their kits makes them extremely vulnerable to ganks and shredded in seconds.