I have played Renekton since i started in season 4. He is a great lane bully to play as, once you understand how to win lane with renekton then you need to pratice what to do late game with him, typically if you are ahead i like to spilt push while my team pushes to get a different tower at the same time. If you are even or behind then you need some tank items and you either want to saved your carry with your W or stun the enemy carry with yout W.
Kled im only mastery 5 on so far (working towards that mastery 7), but Kled is a lane bully too, but Kled excels at tower diving with his team (due to his mount Skaarl). Kled just takes a lot of prstice to learn when you want to not fight, because Kled wants to always fight you need to be a good judge of when you can and can not fight.
Falling behind as Kled hurts a bit more than renekton. Renekton has a point an click stun so even tank renekton has something to offer to his team, Kled if he is behind is not much more tha meat shield.
I love both Renekton and Kled. I think Kled is a little bit stronger than Renekton once you fully understand Kled
Illaoi is pretty good too, i personally dont like her as much though because she has zero hard cc.
Hoped i helped a little bit. If you have any more questions about Renekton or Kled i will do my best to answer them