I bought a 5 door as we can't get 3 door GTis in NZ.
Thought, as most do, that a 3 door would look better but not so sure after seeing a few Ed30s around.
Think they are on a par really - and the practicality of the extra 2 doors just about swings it.
At the risk of starting another debate - go for the lighter colours - candy white or silver. The detailing stands out more in the lighter colours.