About GPU

Hey guys, I want to grab one more GPU soon.
So some guy on other hash cracking forum told me Radeon is better than Nvidia because it has more cores?

I have currently AMD Radeon R7 240 2gb ram 128bit

Now what should i grab next? Nvidia or Radeon ?

I mean which one is better really of them?

I'm going to use it only for hashcracking bruting actually.. What do you suggest me?
I'm looking for something up to 300$