With GPUs to avoid it's a bit of a mixed bag - the specific brand to avoid 100% is Powercolor regardless of what core it runs. They're the most common GPUs to have instability issues and many users will outright not get any video out past the Clover bootscreen making a macOS install virtually impossible. XFX should also be avoided if you can, because people also have trouble with it, although most XFX cards will work with CSM/legacy mode turned off (XFX cards have an issue with VBIOS, but the UEFI VBIOS is fine.) (Though it is possible to get the XFX RX 460/560 working with a VBIOS flash, it's risky and not recommended). And while Sapphire may be the best brand for Polaris GPUs, Vega GPUs are quite a bit of a different story. While many have working systems with Sapphire Vega, a good chunk of users also experience instability and issues with macOS functioning correctly. Update: With the advent of macOS 10.14.5, support for Sapphire Vega has been greatly improved. But do note that these issues were quite serious so tread lightly as all the kinks may not have been truly resolved
All 550s will not work except for the Sapphire Pulse 550 640 SP, as the other 550s are Lexa core, while the Sapphire Pulse 550 640 SP is Polaris.
And for those who are wondering why this list contradicts Tonymacx86's buyers guide, remember that their bottom line is to get users to buy hardware through their affiliate program. This is also the same website that recommended Pascal GPUs 5 months after Mojave's release, would you really trust a website that's neither kept up-to date and offers shivers the beast tools?
Powercolor(AVOID ALL MODELS)
XFX(AVOID VEGA AND 590/560/460 MODELS)
HIS(AVOID ALL MODELS)
VisionTek(AVOID ALL MODELS)