I just found this great site which has great comparisons and reviews on the new Lancer Evo and the new Impreza WRX and Sti. I like his views since he is an unbiased source from Hong Kong, and sticks to facts, not feelings. His entire site rocks, and he gets no income from it what-so-ever.
Review of Sti and Comparison:
<http://www.geocities.com/MotorCity/Track/9120/html/Subaru1.htm#STi vs Evo>
Review of Evo:
The editor feels that Evos performance is much better than the Subaru WRX, and also better than the Subaru Sti. The only drawback on Evo compared to the Sti is that the Evo has a 5-speed while the Sti has a 6-speed (WRX has 5-speed), and the Evo rides a little rougher. He feels that the Sti is the REAL competitor to the Evo. I feel the same since they should come out in the US at about the same time (some time in 2002) and equivalent performance.
I think the only thing left to consider is the reliability of the two. With the new Mitsubishi restructuring and Global market targeting, you never know they could match Subaru.
Clearly the EVO is better than the WRX, but STi now there's the comparison. Apples to Apples I say.
In my opinion I'll sacrifice a little reliablity, and even interior quality, for a great looking exterior. Evo VII has my vote, and money is waiting for it.