My GTI is not a PP, but my previous was a GTD, so here are my thoughts on those differences. I respected the GTD as an awesome piece of automotive engineering. Plenty of go, due to the torque available, and a comfortable, solid, safe car, which would get me anywhere, pretty much as quick as todays roads will allow. The only thing it lacked was a soul - I never loved the car - it never got "inside" me. Because of that I changed, at 2 years, into a GTI with DSG, and I've not looked back, except, maybe, thankfully.
Proper engine that sounds great, revs out nicely and just seems a fair chunk faster, mostly because of the power delivery. The car always feels to be just on the end of your throttle foot, with instant response always available and the loss of a bit of weight does no harm to this, as well as helping the steering feel. In short, the GTI has a character that the GTD lacks.