You see, the hilarious part is that I do these things! it seems to have little to no reward aha. This isn't an elo hell QQ type deal but I put my best efforts in, I understand objectives etc but sometimes the weight is just too much to carry at my elo.
Ok, i think you should try amumu. While he is considered a tank, he deals a lot of damage, clears fast, does infact snowball a little but kills arent essential, Strong/Easy ganks and even if you fall behind a little you are still incredibly useful all game. His Q, W, E, R combo deals rediculous damage to the team considering just the base damages as well as his W deals % health damage which there is a ton of in this meta, making him even stronger since people are stacking less resistances than last season and he was considered near god tier then.
Personally, my first jungler was warwick and I loved playing him. He is a very easy jungler to pick up as he has endless sustain in jungle and with red buff and his w, he is actually a decent ganker as you can constantly apply red buff to the enemy while they run. Post-6 his ganks are pretty much guarenteed to secure a kill as long as your team is there to follow up. He can build incredibly tanky and do a decent amount of sustained damage. Plus the W gives a giant attack speed buff to your entire team which is great in team fights. He has fallen out of favor with me though as he pretty much only works in lower levels of play as people know how to deal with WW later on.
Out of all your junglers, my pick would be for Xin Zhao though he is unfortunately getting a (much needed) nerf soon. Xin Zhao has amazing clear speeds and can easily gank at level 2 or 3 if you have the skills and get an early red buff. His sustain in jungle is amazing and you can build him incredibly tanky and still do an amazing amount of damage. Plus, your gap closer is great for jumping on carries in a team fight and you can ult everyone away so your team can burst down that one important target. I'm currently in Silver 4 (almost silver 3, currently in series) and I'm doing incredibly well as Xin. I have around a 65% win rate with him.
Maokai is another great choice for starting junglers as his clear time in jungle and sustain are both pretty great. In addition, that lock on snare followed by your knockback slow sets your teammates up for a great gank. However, a Mao cannot carry a game even if you build him AP, you can only be a giant wall. His ult is amazing for teamfights and his utility is always great.
You have some pretty great choices for junglers that I wish I had (I'm currently maining Xin, Hecarim (ponies OP), and Olaf). Nautilus and chogath can be amazing if you can land those skill shots well. The issue with nautilus is that his clear time is still pretty slow in S3 but he can do a decent amount of burst and singlehandedly CC-lock a single target. I tried jungle Kha'zix once but even with runes and masteries, his early clear time isn't where i wanted it to be and he is incredibly squishy so you are out of pots by your first clear. However, Kha'zix is a pretty good ganker post-6 once you get the slow on your W and it greatly increases your clear time. I refunded Kha'zix for hecarim though and I have no regrets.
Don't buy shaco unless you are positive you like him. He is for very experienced junglers who know how to counter-jungle well and you will most likely get destroyed if you don't have a good early game. However, a good Shaco can be a scary force in the game as you put pressure on the whole map with the threat of your amazing ganks from absolutely nowhere. Only buy shaco if you are confident in jungling though.
If you want a strong jungler to practice, play amumu though he is banned in almost all ranked and draft games. He is tanky early so he doesn't burn through his hp pots. His clear times are good, and his ganks are scary even pre-6 if you are good with that bandage. If you get ahead, an AP amumu is almost unstoppable as you just have so much burst and sustained damage with your w and e.
These are just the opinions of a Silver level player though, if you want an expert's opinion on jungling, go watch stonewall008's vids on youtube (he makes the jungle tier lists). I've been watching him for months and it has greatly improved my jungling. Also watch some pro players stream jungle (oddone is great).
Good champions to start with are xin zhao and nocturne are easy to learn and can carry games. Try to gank after lvl 4, it's save because you have most of you abilities. If you are bellow 50% of your health and go to base and buy madre razor or spirit stone.
EDIT: the more you jungle the more you will learn. If you look up some videos from stonewall008 you will learn a lot from him.
for runes you can use armor seals, and attack speed marks are always a great start and will work on almost everyone.
Watch some streamers that jungle exclusively, try to pick one that talks about what he is doing. That should help you learn tons of stuff. Make sure you watch more than one, you'll get a wider variety of information. watching streams really helps.
If you want to know who to try to learn, check the tier lists. Currently Hecarim, Xin Xhao, Cho and Vi are the strongest junglers in my opinion. A good jungler champ will be able to build cheap tank early and hold off on getting damage til late. Look for kits like that.
The general jungling guide someone posted earlier is also a good guide, I've read something similar and it helped me immensely.
Lastly, if you want someone to play with who knows a little more, feel free to add me in game. I main support but jungle was my secondary role for a long time. recently I haven't even been playing much ranked, but hit me up for a normal sometime.