As I understand it, the difference is the bump-steer. A car with level turnbuckles will typically have a small amount of bump toe-in, its never much but in a 1/12 scale car a few thousandths can mean a lot in how it runs, while a car with the angled servo and turnbuckles will have a small amount of bump toe-out. The difference as I understand it is that the bump toe-in will make the car more aggressive in the corners when the front suspension compresses and the bump toe-in effectively turns the wheel more in, while the toe-out will make it more mellow by angling it out slightly. Just last weekend I went from a laydown servo arrangement to an angled one and saw no real difference in the cars aggression or steering throw needed to make it run.