Sej is one of the best junglers, but you must use others as well. She gets banned a lot. Try evelynn and hecarim is also very nice (amazing ganks and tank, can carry games). Jungling is the most fun position, in my opinion. You don't have to worry about last hitting or some guy constantly harassing you in lane. You also get to feel like a commander. Your job is to clear camps, gank, countergank, keep tabs on the enemy jungler, keep tabs on the enemy laners if they roam, take out wards, coordinate so that your team can take objectives like dragon, and overall shot caller. That's a lot of things you have to do :P.
I've never tried udyr or jace, so I cannot tell you about them. I know udyr can be really good early but falls of late because of his bad teamfighting.
Start the camp nearest to adc lane, then go blue and then either wolves or red, depending on your health. Choose runes carefully. Gank the lanes that are getting shoved into your tower.
Is very good. She has fallen off competitive play but is still used. Her ganks pre 6 are very weak and after that they are not great, but the ult helps a lot. Don't take flash with her because your ult does the same thing. I recommend exhaust but you can try tele for map mobility. Exhaust helps in ganks. She is great at counterjungling and amazing at teamfights, both at initiating or jumping right in the middle of the fight. Just your W in dragon form can burn through the enemy team if they are grouped up. Her clear speed is amazing. You can do every single camp without having to back at level 1.
Is just freelo, which is why she gets banned a lot. I went 7-0 when I bought her before losing. She is a tank, so build accordingly after getting your jungle item. She has great ganks with her q. Her ult can turn around games. Land a good ult and watch everyone in your team saying ''omg I love you sej''.
Can get counterjungled early, but she has good clear speed and great early game due to her passive. Also build tank with some offensive items too (very common to start with hexdrinker, but trin force is also great on her).
More common to see him top, but I think he is an amazing ganker. He has good clear speed. He is a tank, so build armor and health after finishing your jungle item and trin force (although obviously builds depend on every game). If you get lucky you can pick someone off at level 2 with your E. His ult is also amazing for ganks and teamfights. Try to first hit with e and then ult for more cc, but you can also start ganks with it. He does not have invisibility, but he can come out of nowhere with his E/Ghost/Ulti, which is pretty much the same thing.
Take
instead if
. His E and his ult are good escapes (not to mention ghost can also help escape).
The reason you take
is because his passive makes it so that he deals extra damage proportional to your bonus movement speed, so E and ghost are great. Additionally, your E deals more damage the more distance you have travelled before hitting your target. So if you pop ghost and e you will go really fast and travel a greater distance, thus dealing a lot of damage and probably surprising your opponents. Going E+
and Q once you hit the opponent can secure an easy first blood at level 2.
Unfortunately ,he also gets banned a fair bit, so don't rely on getting him every game. Top laners with higher peak can also take it first (and I would probably let them and choose something like an eve instead.