I've got Avon ZV5s on mine and they're great. Helps that I got a mate to get me a discount and so had two fitted for £150!Well worth the money, loads of grip and they last well.
The GTD is like a blow up doll. The GTI is like a proper woman. Sure the doll might last longer, and the woman might have higher running costs, but which would you rather have?
I had a mix of Avon ZZ3 and Dunlop SP 9000 on the GTI when I bought it and they weren't as good as the Potenza's I had on my last car.I wouldn't fit any of them again, for different reasons. Look into Falken FK452 (cheaper) or for or Vredestein Ultrac Sessanta, which people rave about.