I have never really investigated before so I can't tell you what each option does.
However, I have always created with the user set to ''Self" and never had a problem.
I think it's one of those settings where non sysadmin users cannot run if you set to a certain value. From what I can see, by selecting "self" you get the package to run as the owner.
------------------------------
The Users are always right - when I'm not wrong!