What CPU cooler is the best choice for a 7800X3D?

Any decent air cooler should suffice for your setup. For instance, the Thermalright Phantom Spirit is a solid choice that many users have had success with.

I've heard mixed reviews about the Peerless Assassin 120SE; it reportedly fits RAM modules up to 42mm, which might not work for you since your RAM is 43mm tall. You might want to look into other options!