Left or Right? Vote now!

Around the world, countries differ in driving practices. Some countries drive on the right and some drive on the left. Which is better and why? Why do you think these differences exist?

I suspect that since most of the people reading this are accustomed to driving on the right, most will say that driving on the right is better. I doubt there's any scientific evidence out there to support any claim, but I'll be curious to see people's opinions, and if somebody's really ambitious, a reference to some Internet debate on the subject.