ahh... this thread reminds me of the last year of my life. I have been debating on the 2005 EVO vs 2005 STI thread for a while now. While being in the market for both, I have had the pleasure of driving both cars several times.
In my case, I decided on the STI based on personal preference of looks and features. Both are a blast to drive.
The EVO has a bit more wild powerband... the turbo spools up and all hell breaks loose. Yes the interior is a bit sparce but hey it's based on an Econo-Box. Handling is a bit sharper in the EVO too. If peak HP numbers are your only goal, the EVO is your car too.
STI has a bit more grunt down low and is the better choice for a daily driver, IMO. I wanted a daily driver so I decided on the STI. I would spend much more time in the lower RPMs than up at redline so the 2.5 liter torque was appealing to me. I like the interior over the EVO and the ride seemed a bit more comfortable for everyday. Plus, the 2.5 boxer is a nice sound to my ears.
All in all, it's personal preference and not much to debate or start a riot over. It's pretty much personal preference.. i know people who daily drive each. I know people who make good power in each. Both squat and take off great.
Now to find one in the year/color/millage/price I want. ha ha Thats the hardest part of it.