Take it from me. My first performance car was a WRX (GDA) which I chose over the GC8 due to the better chassis. If I had my time again, I would've gone with an Evo 7-9.
WRX's have too many weak points and are too difficult to get power from.
I spent a fortune on mine and only netted 220kw at all four with 19psi of boost.
I decided to go WRX over Evo as the symmetrical AWD appealed to me for weight distribution. I didn't like the E-W mounting of the Evo.
Had my WRX for 2 years and hung out with the Evo Oz crew (Rexnet guys aren't as social). Had a heap of fun and found out just how much better the Evo is.
Normally I'd scoff at electronic aids but the Evo's AYC, ASC, ACD & S-AWC make it unbeatable in the twisties (which was what I was into at the time).
There appears to be more aftermarket support for the Evo too so upgrades are easier to find and cheaper to buy in comparison to the WRX.
Do some research on Evo Oz. I've learnt that the 5MT's are stronger than the 6MT's (opposite to WRX) and the AYC/ACD pump is a bitch to bleed!
I still have a soft spot for WRX's, must be that boxer note but probably wouldn't buy another.