Flip a coin Tightwad. :laugh:
I’ve done both. However since most of my hives are foam based and pretty well insulated, it kind of defeats the purpose of insulation to have one whole side of a structure open to the cold. Since foam moderates heat in the summer, I also keep the screens closed in the summer anymore.
For winter, the best configuration (compromise) I’ve found is to use a smallish top vent to vent moisture. The idea of bottom venting just doesn't make any sense to me. I’ve seen too many human bathrooms (moisture environment) filled with mold when a top vent is not working.