most forums are biased, ive never had either, but have driven both. so ill give you my unbiased opinion.
GTI has a much better interior, IMO the leon looks much better. My problem is that every golf i come up near always looks like a GTI, until you see it has TDI on the back. Not distinct enough IMO.
personally in your position i would have the cupra. half the mileage and newer, with the k04 engine which is ALOT better than the k03 when it comes to tuning,
the main problem with the golf is your paying a surcharge for the badge( and maybe a better interior)
the curra has depreciated more, but comes with better brakes and a superior engine