Depends when you want to be strong and what your playstyle is.
Kog is probably the strongest AD carry right now.
Urgot is also a popular pick as of late.
A lot of people are suggesting Vayne. Shes alright, but suffers from a bad early game. Still has a great late game.
Caitlyn has one of the best mid games. At level 11 she is a beast.
MF has one of the best early games and you can snowball with her if you're good.
Graves has a good early/mid game.
Ashe has the best initiate in the game with her ult. And is like the only AD carry that can initiate a fight.
Corki is pretty mobile and has probably the best escape of an AD carry in Valkyrie.
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