Yeah, you really cant go wrong with either. In this case, that evo sounds like a good deal but I think it cmes down to what you plan on doing with the car.
If your looking for a more dd than not just buy an STi, go cobb stage 2 and stick with some sound suspension mods and you have a car that can hold its own in any form of light motorsports. A stage 2 STi,is a great value. But then again im sure the evo has its same equivalence, so I guess it would just come down to a matter of reliability to me, which I would give to the STi.