Right eye.
If I were left-eyed, I would train myself to shoot right-eyed. So many rangefinders have the viewfinder all the way to the left side of the camera, so that your nose isn't fighting against the camera, and so that you can see the rest of the world with your other eye, that it just doesn't make sense to use the left eye. (eye performance being the exception)
This little ergonomic detail is one of the things I like best about rangefinders.
When shooting any kind of action, you will find that you get a higher percentage of well-framed shots if you keep both eyes open to better predict when & where the object will enter the frame.
Interesting tidbit: When I was Army basic training in the mid-1990s, they did a test on each troop to determine if we were left- or right-eye dominant. I'm right-handed, but they said I am left-eye dominant. So I took their suggestion and tried shooting the M16 with the left eye for the sight. I couldn't hit a barn that way, even after a full day of trying. With my right eye, I could hit the 300m silhouette pretty reliably. That may have to do with the extra difficulty of having the rifle in my right shoulder and having to crank my head all the way around to use my left eye...
With cameras, it is much easier to mix it up, (i.e. right-handed, left eye) as they don't usually have shoulder stocks to get in your way.