depends what you're doing. i usually have mine around 33-35 for daily driving. if i'm racing, 38 psi (cold) seems to be the magic number (around 40-42 psi hot). that's on the stock re92s, different tires will need different pressure.
I believe Subaru recommends 33psi in the front tires and 32psi in the rear tires (on cold tires). I am running at 34/33...no reason at all, I just like being 1psi over what the manufacturer recommends.