Insert vs Update

First off I apologize if this is question has been beaten to death. I've
looked around for a simple answer and could not find one.

Given a database that will not have it's PKEY or indices modified, is it
generally faster to INSERT or UPDATE data. And if there is a performance
difference is it substantial?

I have a situation where I can easily do one or the other to the same
effect. For example, I have a journaling schema with a limited number of
"states" for an "entry". Currently each state is it's own table so I just
insert them as they occur. But I could easily have a single "entry" table
where the row is updated with column information for states (after the
entry's initial insertion).

Not a big deal but since it's so easy for me to take either approach I was
wondering if one was more efficient (for a large DB) than another.

Thanks!