That's really weird - I started playing electric more than acoustic for the past year or so, and at times I dabbled in classcial, so I realized that I've forgotten completely which leg to put the acoustic on. I think I put it on the left leg now, and it seems more comfortable that way, too.

I guess for a strumming type guitarist, the right leg is better, since you won't really be playing anything higher than, say, the 9th fret. But if you're going to be playing things all over, the left leg would allow easier access to the higher frets, in my opinion.

And, I remember reading in a classical guitar textbook that the goal of positioning the guitar is to center the twelfth fret with the center of the torso. Some people even would rest the headstock on a table located to their left, but that is an entirely different matter.