Unless you need serious balls to the walls, an STI is not necessary. I think a WRX is perfect all around more enjoyable, especially as a DD than an STI would be. I'm having a hard time contemplating the WRX as my new ride after the GTI or I go SUV for the first time in my life...
I've been sold on Subaru since I've seen the amazing beating my sister's boyfriend puts on his Legacy and the damn thing will not die. It also went thru some of the craziest snow storms NJ has seen in a while where all the other cars were in ditches on the way to work. They are awesome all around cars.
Yeah, they're different cars, even more so now with the different engine. For me, low end (ie usable) torque is much more important, so the wrx is the better car for me. It doesn't hurt that it's significantly cheaper, either. I do wish it had a bit more power, but it's fast enough, and hopefully tunes will start coming out soon. As far as going from a gti to a wrx, it's not as nice on the inside, but it's a lot more fun to drive, so it depends what youre looking for.