In low contrast lighting - exposing ISO 100 film at 200 isn't going to lose any shadow details - ISO 100 @ 200 best choice.
In high contrast lighting - exposing ISO 400 film at 200 will gain you shadow detail that you would have lost shooting at 400. ISO 400 @ 200 best choice.
I normal lighting - You could lose some shadow detail with ISO 100 film used at 200. ISO 400 film used at 200 is your best choice here.
It ALL depends on the lighting how you expose and process you film.