Udyr, Olaf, and Chogath.
Problems with them as a whole.
Biggest problems right now: They has no damage if he builds tank, and has no survivabilty if they builds glass cannon. So why is that bad? Well tanks that are viable either A: build tank and still do damage(Rammus, Maoki, vi, and jarv(kinda)) or B: build damage and have a way to apply it very well and reliably or at a low risk(Lee sin, Kha zix, wukong, vi) So where are all of the other junglers in the game? Stuck between itemization hell, and a lack of reliable impact on the game.
Olaf: He not only is required to build damage to impact the game later on, but cannot itemize ANY attack speed or he loses effectiveness. The amount of micro needed to use axes, , E's, and autos while dodging stuff or on a moving target is staggering. He basically cant do it with any attack speed or at lower HP's its almost more effective to just auto and forgo E's completely because of the animation timing.
Olaf suggested change: take away some attack speed, and give him a more manageable steroid. Maybe change his heal attack speed thing from 80% extra attack speed to a on hit ad damage steroid, that makes it so you take 4-20% extra physical damage on hit. or extra tankiness if someone is slowed by an ax. Right now his steroid basically makes him attack SUPER fast. So fast that using your abilities at all is usually a waste.
second Olaf suggestion: Reward Olaf more for building offense. Right now a 80 ad steroid and 80-180% increase to an already capped out starting attack speed(.694) scream to build crit, armor pen, lifesteal, or something like that. But you receive almost no benefits for doing any kind of attack speed based items(cannot cast abilities fast enough, lose dps.) or if you build just ad your e and q barellyyyyy receive any bonus. Why not make his e scale off 100% ad, then nerf it to 0-160 base value that returns 40-20% of the damage back to Olaf. Because right now it feels awful to use anything but autos whenever you itemize any offense. or make his q base value go from 40-200, but scale off of 1.6-2.0 bonus ad or something. Landing consecutive axes should be rewarding, not make you annoyed that you have to do it to auto the enemy. Using your e and q mechanics properly on moving target should be a powerful way to kill them. Right now it feels like a hassle thats just as effective as just landing an ax and then smashing youmous or whatever item and waiting the 2 to 1 sec's before throwing the next ax to then again just let olaf auto them at hyper speed.
Udyr: Udyr is actually not a bad solo queue pick, but he just cant do it because of the meta more so than the other two. He doesn't need buffs. Instead the junglers should receive some value for having SUSTAIN, and DUELING potential. Instead right now its just whoever has the most reliable ganks. Which sucks whenever there is a whole other aspect to jungling in counter jungling, buff control, dragon control, and scaling tanks. Right now kha zix or Lee sin are infinitely more likely to get dragon and your buff by ganking bott and getting a kill then you are from killing a jungler in his jungle.
second problem with Udyr: The free wards from trinkets and free xp from jungle minions. Let me tell you that there is nothing worse than being on the same level as the other jungler when you have 50 more farm and a kill over them. Getting extra xp from jungle creeps is the worst mechanic in leagues history. It basically ENSURES jungler presence and strength throughout the game. Gank messup? Here is a free 50% increase in xp since your a few levels down. Clear the jungle once and your good to go again. Have 30 minions at 20 minutes in? doesnt matter, each one of those were probably buffs that gave you 50% extra , so you aren't under leveled at all. Thank goodness your a level based jungler like lee or kha zix. You can impact the game no matter what happens! You might argue that is a good thing, but laners face way more risk and have none of the same forgiving mechanics. Which removes one of the funnest parts of league: being rewarded for doing well. If you do well you deserve some kind of reward. Not having any reward(either you becoming stronger or the enemy becoming weaker) sucks.
Cho gath: He needs a reliable way to impact the game. Buff his base attack speed, and maybe increase his attack speed per level. That way if cho gath's skills are dodged he can do more than just....well nothing. At least he can auto people. OR maybe buff his E's ap ratio, and value and nerf his other twos. That way he cant passively waveclear forever after a certain point. This one is way easier than udyr's or olaf's changes to do. Cho gath just either is a cc BEAST that's op, or does nothing at all. Make him a little more reliable and don't take away counter play he has right now And I think he could be a really healthy champion in league.
TLDR: Olaf needs less attack speed. He needs more reward for doing his mechanics correctly. Jungle itemization should help attack speed based champions more for interacting with enemy, like counter jungling. Or you should not get any bonus xp from being behind in jungle. Cho gath just needs a reliable way to impact the game. Like better autos, or.... well better autos really. Giant monster should hurt you when it hits you.