Actually, historically touring cars have been based on Saloons (or Sedans) of one sort or another. GT Cars are usually sportscar-based. Although, to confuse things even further, the SuperGT series has its roots in the old Group A Touring car regulations, which were killed off by the success of the R32 GTR.
From what I've learned, the "touring cars" (be it JGTC, SuperGT, GT500, GT300, WTCC, DTM, etc) are supposed to be the way for car companies to show off their mid level luxury cars. Some are for lower tier cars, but most are middle class and luxury vehicles. The best touring car, with that in mind, will also project onto the road. Mercedes CLK Touring Car would be my answer. I wouldn't necessarily choose a MB otherwise for many things.
