Not necessarily pros and cons, but some things to think about

- Where is your expertise? If you have primary APEX expertise, then perhaps keeping the code in the database makes for easier maintenance etc. Conversely, if you already have email routines/infrastructure etc at the Linux tier that you're using extensively, then maybe just add to that.

- Transaction requirement? Do you want to email as part of a transaction? If so, then you really need to doing that in the database

- Any email specific features you get with one option over the other? eg schedule mail times etc etc

- Any infrastructure limits/costs? Do you save network etc charges by choosing one over the other?

- Logging. Does one option give you better auditability over what emails were sent and when? Email history can often be critical down the track.