Unfortunately, I never drive with Porsche, however have tried TT 2 months.
Concerning TT, I can truly say, that exterior is very, very intresting, but interior it is the same as Kia

spare parts - no problems accured.
Boxter is more expesive, that TT and S2ki
I`m drive with of course S2ki and Audi A4 1.8 TQ S-line.