I had a left zipper and I will never have another. Right zip works soooo much better for me. I sleep to the left in my Sawtooth and I can open the zipper and reach out and do things without lifting the bag completely off. I can light the stoves or get a drink without loosing all the heat I've built up in the bag. I'm right handed so sleeping to the left puts my strong hand on the side where everything is at. If I was a leftist I'd have the zipper to the left.
BTW , I have a Western Mountaineering bag so the zipper always works and doesn't snag so working it with weak hand is no problem.
I'm left handed. Zipper orientation is not very important to me.
Seems to be a little nicer if the zipper opens towards the middle of the shelter for entering and exiting. Not a deal breaker either way though.
I have a right and left hand on my body, so it doesn't really matter to me. If my shelter only had one entrance, or I was restricted to one sleeping orientation, it might make a difference. Otherwise I just set it up so it opens towards the exit. I'm left-handed and most of mine are right zip, but that's just the way they came. I also use a quilt now, so there's no zipper except on the bottom underneath my pad, and both sides are equal.
Mine is left but it only matters when getting in because I toss around all night and my zipper ends up on my back, chest, other side etc. I can't lay still in mummy position. I'm gonna have to look into getting a quilt
I had a quilt and I froze in it and much of the problem was that I tossed and turned and every time I did I'd get a big draft of cold air where I pulled the edge up. When I toss and turn in my big , roomy WM bag I don't get the big draft of cold. If I slept still I think a quilt would work great. I also woke up with a frozen arm and hand where I had stuck it out from under the quilt while asleep. I did not have a good experience with the quilt I had.
I prefer the zipper on the left mostly because I have been assigned the left side of the bed (when laying in it) for as long as I can remember. So, I am used to having space there when I need to kick a leg out or whatever.
First 4 bags I've had were all right zip. I am right handed. Thought I would try a left zip and was worried that I would hate it. well the last 2 bags have both been left zip, will not go back to right zip.
Ive never really thought about it and out of the 5 or so bags I have and have used a dozen or so times each I really cant even recall what side the zippers are on. Guess it really doesn't matter to me .