Hi, its unfortunate that you have to part ways with the Porsche but hopefully you can replace the smile with something just as fun, or at least allmost as fun.
Heres how I can help, I consider my self to be a fairly good book resource for the vehicles you listed above. I am far more into the driving pleaser than most kids my age who would rather just have the looks and the straight line speed. I also gather all my research from many many magazines as well as TV shows, but I have never been able to have a drive myself. With that said here are my thoughts as well as some of my compiled research on the cars.
The Sti. The US spec Sti comes to the table with 300hp and 300ftbls, of the group this is the most powerful of the bunch. Its engine displacement of 2.5L is more than the Mitsu's giving it a bit more low down grunt and also letting it rely less on the turbo boost. From what I have heard, maybe others can back me up on this, the Subaru grib is, with lack of a better word, god-like. Very sticky tires as well as a well sorted suspension and AWD system keep this car glued to the road. With all great things there are weaknesses, first a big thing for me with the STi is that, at the limit, it understeers. The car also is said to feel a lot heavier than its competition even though the Evo and the STi share the same weight. Anyway on the the Evo.
Since the Evo's quailties are fairly similar to the STi's I will just cut this down a bit. The Evo is amazing fun, you can just chuck this into a corner and it will just give you a wild ride and at the end of it you, and the car, will be okay. It doesnt have as much power as the STi does but never shows this, in fact the Evo seems to be a bit lighter on its feet. Down sides for the 8, first the lag. The very large turbo combined with the 2.0L of displacement mean you wont have a ton of power until after 3500rpm but after that the thing sends your eyeballs through your headrests. Second, the Evo has a 5speed box, fewer gears mean longer gears means that you will have to rev it harder and father to stay out of the 3500rpm dead zone. In my opinion thats a good thing.
And last but not least the R32. This car is a very cool car, great naturally asperaited motor, killer sound and very much respected a little more than its rivials. It is much more of the sutel supercar, looking very much like the other golfs. But then again it doesnt have the aggression that the spoilers and scoops bring with them. The drive isnt, from what I hear, as invigorating as its conterparts either. But what it trades for those things are a simple lined chassis that you can drive around town without the cops beening the wiser but at the end of the day you can take the long way home and get the lead out.
With any of the machines you are making a good choice. There is no right answer just good ones. But if I had to choose, which it would probably require a spirited test drive, I would end up with the Evo. I am a huge Subaru guy, but the Mitsu is just too much fun to pass up.