Both Nvidia and AMD offer GPUs that compete inside the same performance and price brackets. Whether you should pick Nvidia or AMD will also depend on if you need specific features that are only supported on one of them. GPU Render Engines, for example, are often tied to using CUDA cores, which are only available on Nvidia GPUs. Some Games might run faster on AMD GPUs, or vice versa.
Check the requirements of Application or Game you're looking to run on the new Graphics Card to narrow down your choices.