As far as efficiency is concern INC macro runs faster than COPY command .
Hence -INC <Include Name> will be better than COPY <Include Name>.
When copy command is used while compiling the program probably you need to mention the library where that include is present. Where as INC macro takes care of pulling the include from appropriate place, like if it is present in corrosponding WIP or general WIP or from production.
I am not sure of this difference let me know if i am wrong.