I've had a TT auto and I now have a TT VVTi Tiptronic. Performance wise...the VVTi (Tiptronic) is supposed to have slightly more torque, my importer claimed it had slightly more power too (due to the higher rev limit according to them) but I havent seen proof on here. I'd say the Tiptonic definately has more go lower down, and the higher rev limit is fact.
Useability...if you like autos, you will love the Tiptronic manual mode (just to clarify, the Tiptronic can be used as a normal auto too). Although only four gears, the button-shift on the steering wheel is great fun and goes a fair way to giving you some of the control of a manual. The buttons are rather small though, and until you get used to it you might get the odd missed gearchange, but once you remember which buttons are upshifts and which are down () and as long as you dont wear gloves its fantastic IMO.