A little help with this

Consider the following method for delivering an email M from Alice to Bob where PK denotes Bob's public key, Enc denotes a secure public key encryption scheme, MAC denotes a secure message authentication code function, and K denotes an ephemeral symmetric-key chosen by Alice A -> B: Enc(PK, K), MAC(K, M) Compare the above method with the Authentication only method of PGP. Which method is better? Justify your