Lee Sin, Riven, Teemo, Xin Zhao, Olaf

The singeds I have seen have actually been doing better when they don't bother to get a blackfire torch which leads me to the conclusion hes only as troublesome as he has always been in 3v3.

Xin Zhao, I think he's op because no one can flash away from him anymore and he gets that life steal sword that steals people's move speed then he gets a frozen mallet or something and no one ever gets away.

Olaf can just build like Xin Zhao same thing only he does true damage and can throw an axe sometimes. Both are really fast in the jungle and really dangerous in ganks and tower diving.

Darius, fiora

Yorick seems really strong as long as he has a melee or ranged autoattacker on his team. Being able to start the battle with a 4v3 is incredibly powerful.

My personal 'god comp' right now would be Yorick, Vayne, Mordekaiser. I'm having a hard time seeing what could beat that.

Darius, Jax, SInged, Olaf, Yorick. You forget about Yorick, but he's really OP in this. People just don't play Yorick, because he's also very boring.
There are also very strong early game heroes, like Lee Sin or Pantheon and very strong late game heroes, like Mordekaiser. But Darius/Jax/Singed/Olaf/Yorick are OP through entire early-mid-late game, so...

Darius - Just way too strong in general. Can build tanky/CDR and still do massive amounts of damage
Nunu - Opens up to alot of strategies, blood boil is broken.
Singed - NEARLY impossible to fail with. Farms his RoA faster on new TT which makes him get his godlike status much faster. Overall perfect champion for 3s! Damage/CC/Tanky/Amazing mid-late/Amazing Farmer. The only way to counter him is to deny him for 80% of his CS early game

No talk about Rammus? No real talk about Olaf? No one even mentioned Elise?
Rammus- ball OP at first alter battle, knockup/chase/get away. Late game he gets a 3 second taunt to make ADC kill himself, ball to ensure no one gets away built in thornmail and an ult that deals dmg to towers.
Olaf- True dmg is annoying AF if you level it first and it's pretty hard to out dmg true dmg early game. Amazing jungler, gets better the lower life he gets the more he hurts making 1v1 scary even if you seem to be winning. Built in life steal and attack, a 3s snair as they run away. And of course ult, making him tear anyone apart or able to run out of ganks.
Elise- Map was made for her, she does %life dmg, has a bush check and attack speed boost to takeout turrets. %life dmg means you can build really tanky and still put out stupid dmg, also torch is like made for her. Her attack speed makes her able to solo turrets earlier then most others, of course not talking full life turrets. I easily avoid many deaths by jumping over walls onto jungle or even creeps being able to avoid or chase after they flash away with low life. It's saved my life and allows decent ganks, chase and 2s of non-targetable. Built in hourglass? If you get both you stand there like a tard but then can be full life when everyone else is half life.

I feel like I would be the only one saying this but I love me some Renekton on this map. I've only lost my lane once and that's because Malz was afk at the start and gave him a double kill when he invaded. I've seen a few AP's top lane and Renekton is the perfect way to catch them off gaurd and burst them down like it's nothing. Although OP isn't the right word,he does well there for sure. Has anyone mentioned Shen yet? I haven't checked all the comments above but he has to be mentioned. Ninjas for life!

Darius, Darius, and some times Darius.