I agree that both can be used safely. And, yes to be clear, NMR here means "less likely to happen" not "better able to handle failure." Unfortunately, AES-GCM-SIV (or AEZ) aren't yet in Go's standard lib.

But, why not use XChaCha20-Poly1305 over AES-GCM in Go? Both are "implemented through the crypto/aead" and -- to my eyes -- seem equally user-proof. Why not take the bigger nonce size?