Ours are open whenever possible. When it gets too hot (>85 in the house), we close up and use the AC, but that only happens for 2-3 weeks every year. Even then, we usually open he windows a night.
I would have voted "none of the above" (well, except for Bacon). I open them from time to time when it's warmish (68-72 or so) outside just to get some fresh air. Much hotter or colder than that and they're closed.
Depends on lots of different things. I like the fresh air, but not sinus congestion or humidity. Dogs behave better if the windows are shut too, they don't hear/smell all the outdoor critters and people. Our A/C broke last night, so unless the repair guy has been there and fixed, it's windows open today.
mostly closed... neither I or the wife do heat well. ('course she doesn't do cold either) Actually I can do heat OK as long as I'm moving and active. We usually open them when it's been cold and it warms up (with low humidity) or has been warm and cools off.
Plus they're all large and near ground level for easy access.
With my house being in ground I keep my windows closed most summer to keep in the cool air. I still haven't installed my A/C unit, but my house hasnt been above 74 degrees. Just been running a dehumidifier to keep the humidity down.