Rule or Function and Trigger?

I am beginning to migrate some functionality from an application
prototype into the DBMS. One of these elements is time stamping row
insertions and updates.

I have been reading about rules, functions and triggers in regards
to this issue. So, of course, now I have myself completely
befuddled. From what I can determine from the documentation, it
makes little difference to the DBMS whether I set a rule on insert
and one on update for each table or define a function and set a
trigger for insert or update on each table.

If this is indeed the case then which way is the preferred method?
If one looks at things from a code maintenance standpoint it appears
the the function and trigger approach is preferable. Is it?

Opinions?

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