Not Updated For Current Season
This is a short guide of these Junglers.
Jax - Summoner's Rift
Today, I experimented Jungle Jax and I realized he jungles much faster than Warwick. I got all the creeps on my side in less than 4 minutes! I get my Counter Strike (E) first for dodge and an AoE. Spam you W and E to jungle faster. The only reason Jax should jungle is that he's not that good in laning in Summoner's Rift. Ranged champions will tear him apart.
Warwick - Twisted Treeline
I find all Warwicks that jungle in Twisted Treeline starts at the small creeps. If Warwick can get a Blue Golem at level 1 in Summoner's Rift, why can't he get the big creeps in Twisted Treeline at level 1? So I tried. It works! And I think he jungles faster than usual. Warwick can also get a Dragon at level 5, which I don't see people often do.
Good luck and have fun! (if it works)
Tell me if this works for you! =D