Editing with 4:3 and letter-box video
 

I am shooting a project that will mix 4:3 video with letterboxed sequences.

This is something I have already seen around, so I wonder which is the best way to proceed about it.

I am shooting with a Sony Z1, to be edited in DV, and this camera allows exporting in whatever size you want: 16:9, 4:3, letter-boxed 16:9, etc.

As I would like to avoid video effects as much as possible during editing, I would like to know if it would be better the video already as it will be shown.

Which is the best routine?