The Application Process

I need to choose one more letter-writer for my applications, and I have two options related to my current position - I could ask my immediate supervisor, who I work with pretty closely day in & day out or I could ask our boss - a VP, who I don't really interact with directly all that frequently. I think they'd both agree and would give a favorable reference, so I guess my question is whether it's better to have a less personal recommendation on more prestigious letterhead, or a letter that's really about me from someone less senior in the company. Or do letters really make that much of a difference at all?