Unless you are a power user who is confident in your ability to troubleshoot weird/esoteric issues and bugs, just go AMD.
If there aren't any specific features you need from Nvidia, like CUDA for CAD/Render workloads, AMD is going to have a higher chance of #JustWorking and will give you awesome gaming performance.
I've got a 6700XT paired with a 5800X3D running Nobara Linux for my main gaming rig. Love it to death, runs everything butter smooth.
For instance, Deep Rock Galactic maxed settings at 1080p, I don't ever see it dip below about 160FPS, and most of the time it's between 180-210, which feels amazing on my 240Hz monitor.
In defense of Nvidia, things are wayyy better than they were even 2-3 years ago, and the majority of folks, especially with older Nvidia GPUs, seem to have a pretty decent experience on Linux.
That being said, I would estimate that roughly 75% of the posts I see from users who are having really odd/random issues with Linux have an Nvidia GPU.