It seemed obvious to me that the question is asked from the pov of laying on the bed. From that perspective I sleep on the left. In our case, it’s because that’s the side with the reading light and alarm clock.
You only have a reading light on one side of your bed? :eek:
Seriously, that idea is as foreign to me as the idea of only one of us being able to use the indoor bathroom and the other one having to use the privy, or something. . .
We do only have one alarm clock (though admittedly, it’s a “dual” jobbie, where you can set two separate alarms), but it’s never occurred to either of us that you could have just one reading light.
I sleep on the left side, which is closest to the door. Looking back over our sleeping arrangements over the years, I’m always on the left side but who’s closer to the door is irrelevant: sometimes it’s him, sometimes it’s me.
I always attributed the bed-side thing to the fact that I’m left handed and he’s right handed, so it’s easier for us to reach things on our respective nightstands. No idea, though, really. It just always seems to happen that way.
She’s after your braaaaiiinnnnnns, of course. 
I have at least a couple of friends who swear the middle is the way to go, sleeping between two ladies.
I have slept on the left side for as long as I can remember (I’ve been married 45+ years). But if we are in twin beds with the bed table between, I always take the right hand bed since I am acustomed to having the bed table to my left and she on her right. But even then, if one of us moves over to the other’s bed (even if just to hug a bit) whoever it is will now switch sides, since anything else feels “kinky”.
It’s not really a left/right preference, it’s a “which side is closest to the bathroom” preference. Currently, that’s the left side (I’m female). In our last 2 apartments, I slept on the right.
switch sides every night. Mostly so we can wear the mattress more evenly, because I’m ~85kg and she’s less than half that.
Right side of the bed. Right handed. It has nothing to do with reaching things on the bedside table. 
I remember reading some research that men generally choose the side near the door, and the women the “safest” side farthest from the entrance.
Female. I’ve slept left and right sides, near as I can tell, the correct side depends upon how the room is arranged. I like having a night table for my laptop, lamp, alarm, .44, back scratcher, lube, whathaveyou.
If both sides have adequate furniture, I’d pick closest to the window and furthest from the door.
Um, the top?
I put “on the left” because that’s the side closest to the bathroom. As I’m the one most often heading that way during the night, I always grab that side wherever we’re living / staying. At our last house the bath was on the right side of the bed so I slept there.
I sleep on the right, so if any monsters break in they eat her first. On the couch though, I always sit on the left as I’m lefthanded and she’s righthanded, and we eat dinner there oftentimes.
Currenntly left side sleeper, the previous 20 odd years I was on the R. Even when traveling I got the RH side. Until we enlarged the bedroom and his stuff remained in the room to the right and my stuff fit in the room to the left. So we switched. The bed size is a queen,i would prefer a king so I don’t have to roll over in situ.