I have been using pin lock kegs for years. I have never used ball locks but the pins perform just as good as ball lock. I like that you can only put the gas line and liquid line to the correct one.
One of the reasons people dont like pin lock kegs is that they are a bit wider, but i can fit 3 into my kegerator easily and would not be able to fit any more than 3 ball locks.
The big plus on pin locks right now is the price, I have only paid between 15 and 20 bucks a pop for my pin lock kegs but have heard of ball locks going for around $50. Being cheaper right now I have been able to get a good stock of kegs to keep a good pipeline going.