I always go with Method Directives first, but if its a fire and forget in your case ParTran Standard Directive is a good candidate it fires when PartTran is done, it is meant for Logging, Async Tasks, Emailing, Notifications etc…
Standard:
Executes when service method call has completed
Executes only if service method completes without exception
Processes batch of affected rows at once
Does not affect data save
Ideal place for integration operations (Audits, Email, Logging, Notifications, API)