I think people naturally gravitate towards one or the other. I started as a kid with a two hander and switched to the one hander after a year. I knew immediately the one hander was better for me. I felt like I could really swing easier and more comfortably on that stroke and the pace and spin I could get with it was much closer to my forehand than my two hander was. Also, I had played baseball for many years before that so swinging with two hands was not foreign to me.
When I teach kids I always have them try both. Most of them don't react to the one handed backhand the way I did. Most of the time they immediately go back to two hands. However, there are some kids that know immediately they want to go one handed, and a very small percentage that play around with both types for a while before they pick. As a coach I don't particularly care which they pick, but I want them to have a clear decision in their own mind which one is for them so they can stick with one and get good at it.
I can still hit a passable two hander, but it's not nearly as good as my one hander. I can hit a better two handed forehand than my two handed backhand, and I never really practice that one at all. Sometimes I will hit two hands on both sides just to see if anyone is paying attention.
