The GTI's handle very poorly in stock form, even with the 17 inch wheel option. All season tires are partly to blame, but too-soft damping, too-small bars and too-heavy weight are also major contributors. They are set up more as a sport touring type than a sports car type. Comfortable ride at normal highway speeds, a little unsettling at high speeds on a twisty highway with that much slop in the suspension.
Both the Vr6 and 1.8t are pretty quick in a straight line. The Vr6 is tough to make a lot of extra horsepower on without FI or really tearing into it. The 1.8t is very tunable. If you're willing to tear the suspension out and start from scratch, its a good engine to work with, tough, has a big aftermarket and makes power for short $$.
Also consider the Focus SVT and the Nissan Spec V in this price range. Shop when the rebates are right and you can get an SVT or a Spec V new probably for what you'd pay for a used MSP. We paid $14.5k for my wife's SVT after $3k rebate a couple years back. Its easily as fun to drive as the MSP. I test drove the Spec V when I bought my MSP and it was a virtual toss up, the Spec was a lot less $$ and easily as fast. Suspension isn't quite as good and looks aren't as good (inside or out), but its a fun rig with a lot of torque. Its faster around town vs. the MSP because of that fat torque band. On the track, its a dead heat.
