i fly both oval and sqaure.
Where i fly at my VGS in the instructor role, we fly racetrack as we are in military machines. We find that the amount of traffic you can get in the circuit varies depending on the runway length; but 4 is no problem.
There is also the rule that on first solo's the circuit must be clear of all over traffic. There are also less places to join as there is no base.
When i fly civvy, i find that people under instruction fly bomber circuits, which aren't necessary (apparently its for spacing!?!), and everyone else flies a sort of normal rectangle size. The only problem is, that people join EVERYWHERE - over head, straight in, crosswind, left base/right base or downwind. And with bomber circuits going on as well you haven't a clue where everyone is as everyone percieves the circuit to be a different size.
However, low level circuits are oval
Racetrack in my opinion creates more accuarate more controlled circuit flying; it also holds a less ambiguity to where the rest of the circuit traffic is! You can also get far more circuits done in 20 mins than you can in a rectangle as there is far less *rsing around going on!
(Im a low hour PPL with high VGS hours) Like ASI i learnt the military way.