What's a good Graphics Card for Rendering?

Collaborations

I did the low poly rocket ship tutorial and it took 4 hours for my system to render it. I render it on the GPU to make it go faster but I want to beef my system because I plan on doing some more work. Here are my specs. What do you suggest?

CPU: AMD Ryzen 7 2700 Eight-Core Processor

RAM: 16GB

GPU: Radeon RX580 Series

I don't really understand how to compare Graphics cards so I don't know where to begin at knowing what a good graphics card is and isn't. If anyone knows I'd like to hear your thoughts.