Get an RTX GPU, I want to see people suffer as they slowly realize that they don't even have support in HighSierra. Let the Nvidia fans die a slow and painful death, let this be a reminder to never cross our lord and saviour Tim Apple If you don't want a headache, stay away from all Nvidia GPUs that aren't Kepler based. Currently(and likely forever), Turing and Volta GPUs have no support whatsoever in any version of macOS while Pascal and Maxwell have their support stopping in High Sierra while also requiring WebDrivers so they're not native GPUs(this is important because that means another point of failure)
B-b-but are the drivers out yet?
For GPUs we recommend, check out the GPU Buyers Guide And for those who are running unsupported GPUs, there's still hope for you! With my patent pending How to disable your unsupported GPU for macOS Guide, even a simpleton like you can experience the glories of Mojave and beyond!
Are there any GPU board partners I should avoid when buying a GPU?
Why I'm glad you asked, most manufactures actually have a pretty good track record with Hackintoshes but there's 2 specific brands to avoid. While it is possible to install with these GPUs, there still is a high possibility of issues arising like instability and black screens:
XFX(may work with CSM/legacy mode turned off, make sure it's in UEFI mode)
Powercolor
Note: AMD Navi support is still quite finiky, with WhateverGreen not being updated yet
GPUs that aren't supported AT ALL
Turing
Titan RTX
RTX 2080 Ti
RTX 2080 Super
RTX 2080
RTX 2070 Super
RTX 2070
RTX 2060 Super
RTX 2060
GTX 1660 Ti
GTX 1660
GTX 1650
Quadro RTX 8000
Quadro RTX 6000
Quadro RTX 5000
Quadro RTX 4000
Volta
Titan V
Titan V CEO Edition
Quadro GV100
Lexa
RX 540/X
RX 550/X
GPUs to avoid
Navi 10
RX 5700
RX 5700 XT
RX 5700 XT 50th Anniversary Edition
Note: Super buggy drivers in 10.15.1
Pascal
GTX Titan X(GP 102-400 Pascal core)
GTX Titan Xp(GP 102-450 Pascal core)
GTX 1080/Ti
GTX 1070/Ti
GTX 1060
GTX 1050/Ti
GT 1030
Quadro P400
Quadro P600
Quadro P620
Quadro P1000
Quadro P2000
Quadro P4000
Quadro P5000
Quadro P6000
Quadro GP100
Maxwell
GTX Titan X(GM 200 Maxwell core)
GTX 980/ti
GTX 970
GTX 960
GTX 950
GTX 750/ti
GTX 745
Quadro K620
Quadro K1200
Quadro K220
Quadro M2000
Quadro M4000
Quadro M5000
Quadro M6000
NVS 510