Hi there,
I think the main readon why i prefer OEM jobs is that you get email notification etc of when the job starts, if it fails etc. Also it allows you do other stuff such as run reports and have'fixit' jobs. IE if the database is down, run the fixit-job that starts it up automatically.

If you think of dbms_job being used to schedule only PLSQL jobs to run, and OEM jobs to schedule database (import/export etc) and OS jobs to run and then you can see the diffrence.

_Bob