Robertson is much more prone to camming out, especially when trying to remove them after they have been in place for a while and a little gunk builds up in the square.
I've been using Robertson but I don't often build stuff.. yet..
Square bits on the other hand drive the edge of the bit against the wall of the square hole. The edge can cut a circle into the screw, and the square head gets turned into a circle by wear. Thus required tolerances are much lower, and screws don't fall off the bit. If they did fall off you'd know to change the worn bit.