Which Champion to Buy?

I am either going to get Riven, Renekton or Rek'Sai. I mostly play jungle and I want another jungler, but I started to play top as well. I really enjoyed playing Riven on free rotation, but I think Renekton looks fun and I love lane bully champions. Rek'Sai is ideal because its a jungler I can play without needing to deal lots of damage. Any help with how to make this decision?