Opinions needed: External data structures - Copy book or physical file?

Folks:

I'm looking for opinions on this one ... which is the best way to
define a reusable data structure. Copy book or physical file?

Both work, but I'm trying to decide which approach to take.

Defining it in a copy book lets me tag it as a template, so the
definition doesn't take up any storage, and also allows me to easily
overlay fields if needed. Since I'm defining it in a RPG copy book, I
can't use it in other languages (not important, we don't have any
COBOL code).

Defining it as a physical file allows me to use the structure in
multiple languages (COBOL not important, but I do have a technique in
for Java that lets me use a PF as an external DS).

Any other advantages / disadvantages?

Thanks!

david