I think both LFS and rFactor deserves to be played. I will run LFS because of the great cars, the great tracks and the great multiplayer. I will also race rFactor because of the great cars, the great tracks and hopefully, the treat multiplayer. And even if rFactor doesn't have great tracks and great cars from the beginning, it is modable and so, in time, there will be great tracks and great cars.
Why chose one when you can have both?