The more I think about it...
...the more 'qualified' makes sense.
Unqualified is nice for simple schemata with a few namespaces.
Otherwise, 'unqualified' is confusing for the developer (e.g. programmer, XSLT author, etc.)
Users won't care because they are suppose to have tools, right?!?
My recommendation:
Make elements qualified (not the default).
Make attributes unqualified (the default).