You are going to get a number of opinions on this issue.  I personally like the tractor seat.  It keeps you centered in the canoe.  Furthermore, if you are in back, it keeps your front paddler from moving off center and tipping the canoe to the weighed side.  I used to have to remind my wife about sitting in the center of the seat.  With the tractor seat, she stays in the center.  I also like the tractor seat because it allows you to get a better stroke without worrying about slipping back in your seat.  Bear in mind that I am comparing the tractor seat to my old aluminum seat.
Westwood