i just had a wrx...which is really nothing compared to STi
my opinion is the looks of the WRX is
when it's stock, and requires a lot to get it to look pretty sweet.
sti stock is good looking, from being around one for so long over the summer, it was a big difference than stock wrx and for 05, it just makes it better.
i think if i had the option, i would get an sti since the fun factor of driving and it being fast, turbo makes up for it's sometimes dull looks.