I liked the 04/05 STi for the styling. I know a lot of people didn't, but I actually liked the park bench wing on the trunk - sort of Superbirdish, IMO. I've never driven an Evo. But I've read that they tend to have quicker, more precise steering than the older STi - and I thought the STi was pretty good. But I **** the styling of the new STI. I like the hatch concept, but that is one ugly ass car, IMO.
Neither car is a beauty, but I think the Evo X(?) is much better looking that the current STI. As far as performance, I like the idea behind the Evo's DSG gearbox. The only reason I'd shy away from the Mitsu is because of reliability concerns. The Subies are pretty bulletproof, if you don't ***** them. The build quality of Mitsubishis doesn't have the greatest reputation.
Long answer to say, I'd probably buy the STI, but I'd wear a bag over my head when I drove it. I had to have AWD with my last daily driver car. So I test drove the Audi and the Jag X-type before I went for a WRX several years ago. I wanted to buy the Jag, but the WRX was the best buy for the money and it's been a fantasic car. And with mods pushing it to almost 290hp, it's one helluva daily driver.