Congratulations on your purchase Maurice. Glad to hear you are very happy with your car.
Which is the best tyre? That's the million dollar question. I don't think there is any answer as to which is the best tyre for a specific model.
New, the GS was fitted with Bridgestone. I have Michelin Pilot Sport 4 S fitted to mine. Not the cheapest but I have found them to be very quiet, give an excellent ride and stick like glue.
I have no experience of Pirelli tyres so can't comment on them. However tyre choice is a very subjective topic and what one person finds to be a good tyre there will be others who disagree. To me tyres are one of the most important pieces of safety equipment fitted to a vehicle and I fit Michelin because imho they are the best tyre, others will disagree. From reviews I have read, the Pirelli is a decent tyre and if you find that to be the case then happy days.
One thing to watch. As you know the F Sport model has a staggered wheel set up and I have found quite a few tyre manufactures do not make a tyre in the size required for the rear wheels.