I love the responses.
If you're serious about becoming a driver - as in behind the wheel track time, not just pressing the gas on the straight-away and off ramps, get a Miata or if your parents are willing to - S2000 or 350z.
An STi or Evo has too much power for a young, inexperienced driver and the power bands are farrrr different than an N/A. Plus, its a waste of car on a 17 year old - no offense intended, just being honest.
Though the RSX-S or WRX are solid choices - for fun commuter cars and offer a solid base for learning about mechanics and performance. Focus SVT, Scion TC and Civic Si are also decent choices. But again, if you're serious, get a RWD car.
And let me know if you want any race school info - I've done the Z06 Experience (both C5 and C6 models) at Bondurant, and the Skip Barber High Performance course with the Lotus.
I'm going back to SB in June for the new Lexus IS-F. If you get a Miata, and your parents are willing spend the money, go to a race school. You'll become a better driver than 99% of drivers. And SB has a program specifically for Mazdas. Let me know, I can probably get you a good deal.
The most significant modification to any car is the driver, nothing even comes close. Numbers don't mean anything if you don't know how to drive properly. And hell, its a sh1tload of fun.
And in regards to the Prius, don't kid yourself. The cost of owning a Prius is very high. Call up your local Toyota and ask how many Priuses are in for Head Lamp ($1800+) work. And they won't use gas under a certain power level, so you don't get to go on any highways or main Boulevards. Disruptive Technology, thy name is TESLA.