Hello,
I suggest the AMD cards, they enjoy the free driver "amdgpu" with good performance (as good as the owner driver), unlike the driver "nouveau" nvidia or the manufacturer does not help much for the improve and let contributors fend for themselves.
Then you have to take into account a fairly recent interesting factor, Batocera has integrated the proprietary driver nVidia to counter this problem (provided you have it in the configuration file).
Now, nothing says that your card if it is very recent will be supported, depends of the nVidia driver version used in Batocera.
In any case a very recent card is not a good investment, because it takes time for linux developers to distribute the appropriate drivers and also the time to the Batocera team to incorporate these drivers in turn.
AMD contributes more actively than nVidia to free Linux drivers, so I can advise you to take them.
Theses cards should work properly :
HD7790, R7 260, R9 290, R7 360, R9 390
R9 285, R9 380, R9 380X, R9 Fury, R9 Nano, R9 Fury X, Pro Duo
RX 460, RX 470, RX 480, RX 540, RX 550, RX 560, RX 570, RX 580
RX Vega 56, RX Vega 64, Raven Ridge APU series
Attention this is only an estimate, taking into account the fact that batocera turns under the kernel 4.18, the architecture x86_64 depends on many factors.
Good luck !
