Nvidea or Amd, which should I buy

AMD is 100% the superior microchip company. I'd go with an AMD hardware

Nvidia is allot better than amd if you have a little bit more money to spare, nvidia generally crushes amd cards in gaming and rendering (in cuda dependent task) and they produce the worlds fastest cards (rtx Quadro 8000)

Depends a bit on what you want to use it for, for games, most of the developers lean towards Nvidia giving it generally better perfomance.
Must say that Nvidia is quite pricey while AMD is not. I used to have AMD gpu's but was not satisfied so I switched to Nvidia.

NVIDIA is x8 better in performance for games than AMD,
AMD is good for processors

nvidia straight down and simple amd gfx are not worth visiting

I would say go with Nvidia typically, but also take into consideration the monitor, I typically go for Nvidia because the monitor I play games on has G-Sync. If you are going for budget probably go for AMD but if you are going for the higher end cards go for Nvidia

AMD i find is much more fair on pricing NVida cards seem to be quite expensive so depends if you are on a budget or not.