Seeking advice on buying Lee Sin or Renger

I got 6300 ip now and just enough for one of them.

I am a good skill- shot player,not need to worry about miss Lee's Q

Main Master yi, kha Zix , shyvana as jungle

Since S5 is quite a big change, which one is better now?

They seems perform quite similar role(mainly focus on early gank,become tank in late?)

Hoping some advices from you.

Thank you so much for reply.