I found this article that sheds some good light on your question:
"To understand how this works, imagine a coaster train reaching the top of a hill. As it ascends, it slows down because gravity is pulling on it from behind. But when the first car makes it over the apex, gravity starts pulling that car down the other side of the hill. Because of gravity's pull, the first car starts to accelerate, which accelerates the second car, which accelerates the third car and so on. In this way, all of the rear cars are accelerated by the motion of the first car, so they all start accelerating at different points along the track. By the time the last car moves over the hump, gravity has already accelerated the first car a good bit. Consequently, the rear car will have a higher acceleration at the top of the hill than the first car did. This increased force essentially whips the car over the top, briefly pushing up on the riders so that they almost fly out of their seats.
For many people, this is the best spot on a roller coaster throughout the ride because all the twists and turns are more pronounced. But in most coasters, you can't see the track very well from the rear car: Your line of sight is blocked by the people in front of you. The visual component of the roller-coaster ride is important because it gives you a sense of speed and peril -- coaster designers intentionally weave the track around all sorts of obstacles to make you feel like the ride is out of control. In a typical coaster design, the riders in the front car get an unobstructed view of all these obstacles whipping past them. In a coaster that has seats facing backward, the rear car offers the best of both worlds -- you get a great view and the most intense ride.
The best seat on a coaster, then, is a matter of personal taste. If you love the feeling of weightlessness, head for the back. If you want the best view of the action, head for the front. The cars in the middle provide the weakest ride, but it's a good bet you'll still have a good time. There isn't really a bad place to sit on a roller coaster, as long as you're strapped into a seat. "