In the USA Left is easier because often the sight lines are better. In countries where the lanes are reversed, Right is easier. It's simple, if you can see more things are easier. If the sight lines on a twisty road are equal and wide open, you are on a very cool road.
There's a lot of difference between a blind left and a blind right. The blind rights are a lot more difficult, there's just not as much space and time to react. There's a minor effect from having the throttle on the right hand but that doesn't change anything.