i track my r33 on a fairly regular basis. i agree with what has already been said about both cars. the r33 with the better 'box and motor is a good advantage, however the r33's do have a fairly poor diff (in my opinion) as opposed to the r32's which have an LSD from the factory?? please correct me if im wrong . i believe that even for a car which is only tracked 2-3 times a year, its a very good idea to have a healthy diff if you wish to get the full enjoyment of a trackday experience. spinning one wheel out of a corner when your trying set a good time is very frustrating....
also, the r33's have a longer wheel base, which can be an advantage on a circuit as it gives you a little more cornering stabilitly in certain kinds of corners (but this is a more technical area which most people wont even think about...).
whatever you do, just make it as light as you can. as has been said, weight is just evil...