Insert vs Update

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!