I'm sure you're asking yourself "Who is this guy? Why do I care what junglers he picks?" Well that's up to you to decide. I'm just a Gold II player who loves to jungle. I'll be the first to admit I'm pretty biased too. I have terrible mechanics so when I choose champions like Lee Sin, I play so bad I might as well be blind. So when I say "Lee Sin is the worst champion in the game and I hate him," maybe you should take that with a grain of salt. My strengths lie in decision making, strategy, and objective control, so I have a tendency towards tanky junglers that let me initiate fights and help my teammates make plays. With that in mind, these are my favorite junglers so far in the preseason:
Dr. Mundo - "Mundo goes where he pleases" is finally true again! He got stomped with the Season 3 changes and has been crippled ever since. With the latest changes though, the extra camp allows Mundo to continuously farm which is what he's best at. Also the mastery changes were great for Mundo. In the defensive tree there is Juggernaut (+3% maximum health), Perseverance (regenerates 3% missing health every 5 seconds), Second Wind (increases self-healing by 10% when under 25% health), and Legendary Guardian (reduces duration of crowd control effects by 15%). These are all so good on Mundo. I think he will hit a sweet spot where he's good enough for competitive play but not so OP that he gets nerfed. My #1 pick right now.
Evelynn - The reduction in true sight helped Evelynn so much. You can't just buy pink wards to shut her down anymore (not like that worked well before anyways). Also she scales well with the new hybrid penetration masteries. Prepare to see her banned frequently though in solo queue.
Shyvana - Since her rework, she's been really hot. She got some needed buffs, and the jungle changes really help her by giving her more gold from farming the jungle. Her ganks were weak in the past due to a lack of CC, but now she can stay in the jungle and come out as a late game monster.
Zac - The mastery changes really helped Zac because he's so health based. The same masteries that help Mundo, help Zac. He can also farm quite fast if you max W first and the new jungle rewards farming well.
Nautilus - They buffed him again!? In the last patch they increased the duration of the root on his passive. He was already awesome and got another buff. He brings an insane amount of crowd control to a fight and this just made him even better. He's got me hooked in for the long haul as my favorite jungler.
Honorable Mentions: Nasus, Vi, and Elise were all still strong picks at the end of Season 3 and I expect them to continue be strong in the pre-season and Season 4.
tl;dr I feel the tanky, farming junglers will rise to the top this season, which so far are Mundo, Shyvana, and Zac. Also the changes in vision helped Eve become even more annoying. Nautilus isn't a stealth champion or a fast farmer, but I love him anyways so he gets on the list too.