I wouldn't say there is one best as it depends on what your doing with it. This is why most sanctioning bodies have wheelbase limits within their classes and Pro touring is such a catch all, it could be anything. I;d also surmise that depending on if you lean more towards the pro or touring side, weight could also be a factor. Pro implies light weight and high speed, touring implies creature comfort.

The wheelbase length of a B body would make a better land speed racer and would not be as good for a cone crusher like an A body. Similarly, the narrow width of the A would work good for both. The short wheelbase of the A would be good for cones but not great for high speed. The width of an E isn't bad for autocross, but isn't great for high speed. Of course then you have to consider the chassis ability to absorb all the particulars you want to shove into the car depending on which side of the equation you want to emphasize. Large tires, drive lines, seating, weight, comforts, storage can all factor into the selection.