It depends what you want out of the car.

There is quite a large difference between the later model wrx and STi's IMO.

The 2002 STi is a much better base to start with (brembos, ej207, 6 speed etc) if you're going to modify, or if you're more interested in performance / motorsport over daily driving tasks. The STi's also generally have better resale.

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-Eliot