Which is better; TAA and fidelity FX or FSR3?

TAA is the standard anti-aliasing technique for most games, basically it takes a couple of frames and averages them together to try and smooth out any rough edges in the picture.

FSR3 is an upscaler, so basically it creates the image at a lower resolution and then upscales it to your monitors resolution. Having this active can increase the framerate dramatically since each frame drawn by the GPU is not as resource intensive, however some people do not like the picture quality created by upscaling images.

TLDR if your happy with the picture quality, use FSR3, otherwise use TAA.