I know I am late to the discussion, but your question is missing a whole lot of essential information. Which resolution are you referring to? What games? Is price an objective? What is the rest of your build?
All these things are essential to give you the best advice, and I am surprised that not more people has touched on this in their answers.
To answer your question as you put it, the best right now is a RTX 2080ti. This will give you the most frames at medium to high settings.
To answer your question as I assume you wanted to ask it, a AMD RX 5700 is really a good bang for the buck for most games @1080p. That is a good starting point. What you need to look for is local offers, around that price point. Sometimes you will get better offers on Nvidia cards or you will get an XT version for the same price as the non XT.
Nvidia alternatives is the 1660 or 2060.
Lastly, you should always check out reviews of the card you consider picking up. There are potatoes out there that you would like to avoid at any cost. Even brands like Asus and EVGA releases products you do not want to buy. Check out reviews!