Definitely AMD. The drivers are actually open source, much better with less bugs and there are no problems known to me. I currently have had a GTX 1070 for the last 5 years, until I've enough money for an AMD card. My setups, especially Wayland based, are riddled with bugs not present on my (Intel based) laptop - which means the only explanation is the NVidia card. The (admittedly: testing on Arch) drivers have broken two times in a year, not making the system unusable but definitely preventing gaming.
On top of that, the 4090 may be 25% better than the 7900 XTX - but it's also 50+% more expensive than the 7900 XTX, which is a pattern which can be seen for every generation and version of GPUs by Nvidia/AMD. Nvidia's equivalents to AMD's cards are generally 25-50% more expensive, with worse performance but better Raytracing and of course DLSS support - oh wait, DLSS 1 and 2 are only for RTX 20 and up, while DLSS 4 is only for 40 Series GPUs. Which means no matter how good it looks, FSR will be the only alternative for almost all players, even those using NVidia cards like me.

Something different: Intel's Arc GPUs would maybe be worth a shot. According to a PC World article, the A770 beats the 3060 even in it's own habitat - Raytracing. It's cheap and gets better with every driver update. It also seems like the Arc GPUs are compatible with Linux fine, though I'd suggest you look up the compatibility with the games you want to play.