Best AMD graphics card that will work in R3.......

I currently have a GTX 980 in my Alienware R2. My nephew just bought the R3 and was wondering what AMD will work in it since they are a little bit cheaper for him. He does not have the graphics amplifer. I told him he will have to take out the front fan to fit bigger cards in it. Whats the best for AMD that will work in the R3?