I assume we're talking large format?!? Have you thought about using neither? I don't.
I use a black (dark colored) windbreaker–rainsuit top (some use a XXXL black t-shirt), with the elastic waistcord snugged around the GG frame of the camera's rear standard, head through the neck (which doubles as, well – a raincoat), This is the functional, multi-use equivalent of the "BlackJacket" darkcloth, which resists getting blown around by the wind. I gave up the focusing loupe long ago in favor of 99¢ store 3.5 diopter (i.e., strong) eyeglasses.