Can't speak for nvidia, but AMD has been improving rapidly since they released full open source drivers. Ubuntu 16.04 won't work well with newer AMD cards, but

Can't speak for nvidia, but AMD has been improving rapidly since they released full open source drivers. Ubuntu 16.04 won't work well with newer AMD cards, but 17.04 works extremely well and there are further improvements coming in future. Anyone wanting to play games on linux should be buying AMD at this stage.