I suppose i will be a little biased since i own a cupra but i'll give it a go,
current car Leon Cupra, so far lost £1500 in 15 months
previous A3 S Line TDi DSG lost £7500 in 24 months
and before that
Golf GT TDi with lots of toys inc leather lost £8250 in 36 months
Golf + A3 lost far more money and i would consider them not that stong on RV, the Leon is much better due to its lower cost price. I sold the Golf becuase it caused me back pain and the A3 was dull, dull dull and i hated DSG. The Cupra, i have no intention of selling it, its brilliant even the thirst for V power doesn't put me off. I did consider the GTi and amost got one, but for me it has to have cloth interior as the leather just looks cheap. Looks wise i prefer the leon, interior, well there are less squeeks in the leon compared to the golf and i actually prefer the dash in the leon, the door panels are a bit scratchy in the leon and genrelly the GOlf and A3 are finished slightly better, the A3 much better than the GOlf but the GOlf not much better than the Leon. If you were to compare the Mk6 Gti to the Leon then i would say its much nicer inside.
Given the coice all over again then i would pick the Leon again, I find it very comfortable, i like the looks and the dash and don't find the build quality that bad. The leon has had 1 fault and thats a broken CD, oh and its much better equipped, the Golf had the wheels replaced, a dash vent replaced and the convienience module replaced, the A3 had to have the door handle refixed twice and the BBS split rims went really mankey.