Open! I really like the breeze almost regardless of the weather. If it's really cold, then it makes my bed a bit more cozy if the window is open, you know?
I have screens on my windows so bugs aren’t an issue, but I find that pollen and whatnot can still get in and I have allergies. So the only time the windows are open is if we really need to ventilate the room for some reason (painting or something like that that’s rare), and this is basically never when we go to bed
When it is super nice outside during the spring and in the fall, we will absolutely keep them open! Unfortunately, here in Texas, our spring is like six weeks long until it gets super hot and same goes with fall in our fall here weatherwise doesn’t really start until the end of October to mid November I have honestly been in shorts and flip-flops on Christmas morning before!!! although that does not happen very often. The cold here usually does not start for real until late January early February.
We sleep with them closed for a couple of reasons. One being that at our old house, we had the kitchen window open one time and Doodle spotted a bird and went to paw at what he thought was the window and tore the screen and was hanging half way out the window. The other, is I don’t like hearing outside things all night or waking up stuffy because of environmental things in the season. If we have to open windows now, we have to either shut the door to the room or lock Doodle away while it’s open.
My windows have screens, so bugs and such aren't really a concern, but I still prefer to sleep with the windows closed. I don't really open the windows very often to begin with
I usually sleep with the window open and a fan in it to cool down my room since I’m in a 3rd-floor loft and it gets stuffy. The only downside is my neighbor dog barks at everything so it ends up waking me up in the morning.
I always sleep with them open, though my partners close them when I'm out and won't notice lol. I love the sound of the rain outside and I run super hot (they run super cold) and the rooms get so stuffy if the windows aren't open!
I'm on the second floor of my apartment building and my window opens to a screen, so sometimes I do. But only during cooler nights that we are fortunate to sometimes have throughout the hotter months.
Biggest problem is that I live near a street where there lots of noisy cars and motorcycles. I don't know why people have to drive sooo loud. >.>
I typically sleep with the windows shut. I don't have new screens yet, so I don't want any bugs to enter the room. Though sometimes during summer when it gets hot at night, I like opening them a little bit just for some cool breeze.
Fall and Spring - depends on the temperatures. Most of the time closed, very rarely just slightly open. I basically sleep under the window and I'm pretty sure the cold air stream wouldn't do me any good.
Summer - usually open. I like to air out the room during the night after hot days. But the noise of people and/or cars often wakes me, and so when I have trouble falling asleep after waking up the window stays closed for a few days until my sleep quality returns to normal.