You want to get a 99-02 due to the option for readily available parts. The 03s have several parts specific to 03 only. and 97-98 are the redheaded stepchildren that weren't really wanted. I like my 99 mainly for the fact that it was the only good year with the cool options and didn't include the VATs PKE security system that would cause problems when it messed up. Its really up to you on what you get but I would stick with a 99-02 model GTP only.

If you want power and plan to mod I wouldn't bother with the GT unless you have plans to turbo the car. Just look for the normal problems GPs have, wheel bearing noise, funny shifting trannys, check for the metal gaskets, if its low miles and has black LIM gaskets you will want to change those at some point in the future, things like this before buying.