I'm a Riven Main and can say that a good Riven can wreck a Renekton easily. You just have to play smart and need some fast reactions. I always just try to bait out his Q (most of the time with fury) and just shield at the right time, so you can Q1 to get in melee range, then you just trade with him. You will kill him or will force him to go B. But if you cant snowball him with kills or EXP+CS lead, it will be really difficult to kill him at Lv 6, 'cause you cant burst him and he will just eat you with his fury, but as long as he doesnt kill you or force you out of lane, you should be fine. I always start with Longsword and 4 pots (i wait for the 4th one, yes with your Q you will be able to arrive your lane with the minions) and try to finish Brutalizer ASAP. I like to play TP against Renekton, 'cause i try to get kills with TP-Ganks and snowball him, its also good if he forces you out of lane!
Besides Riven i just can agree with the Trundle pick. With LS Runes you got way more sustain than him, the AS boost of your W, the low CD and AD boost of your Q are Renektons nightmare. And at Lv6 he is completely ******, 'cause of your ult.
Pantheon is also a really good pick, just start with a Longsword, 2 Mana and 1 Health pot, you will wreck the **** out of him with your Q poke at the early levels.
Irelia is also a good pick with her true damage and sustain.
You actually can win against Renekton with every Toplaner, it just depends on your skill.
I hope this will help you.
