Thanks all. It's only been a few days, but already there are things that the Tiguan does better than the Golf and visa versa.
Tiguan Plus Points
Ride quality. As my GTI had DCC, it was pretty good in comfort mode (even on 19" alloys), but I have to say to being mighty impressed at the Tiguan (again with DCC) even though it's on bigger 20" wheels. The ride is simply superb, very cosseting but also not too loose over harder ground. It's also extremely quiet (eerily so in fact), with hardly any road or wind noise.
The panoramic sunroof is a revelation, pretty much covers the entire roof and tilts and slides (with an electric sunshade also).
Nice to have 30 colour ambient lighting in the doors and also in the back door too, makes it look really classy at night.
Having wireless Apple car play and wireless Android Auto is brilliant and works seamlessly and very quick to connect.
When in normal driving mode (not Eco), the car seems to have coasting built in, as when coming off the throttle, the revs drops drop to tick over.
GTI matrix adaptive headlights were very good, but the Tiguan's IQ fully adaptive lights are another level, and i feel that on main beam I could illuminate the moon !
Front brakes on the Tiguan seem massive compared to the GTI which had 312mm discs, whereas on the Tiguan the calipers are much bigger, and it looks like these are 340mm ?
GTI Plus Points
There's definitely been some cost cutting in some areas of the car. For instance, the GTI had a flocked (velvet) lined glove box whereas the Tiguan's is hard plastic. The A-Pillars on the GTI were soft touch materials whereas on the Tiguan they are not. Finally, the vanity mirror lights on the Tiguan now look super cheap white plastic jobbies and nowhere near as nice as on the GTI.
The engine cover on the Tiguan is a featureless cheap bendy piece of plastic (with no markings at all), where the GTI had a rather nice engine cover. I know this isn't a major point as the bonnet is closed most of the time, but it still cheapens things.
Even though the GTI had more power, the Tiguan is still worse off MPG wise (was expecting this), but to be fair it's only got 250 miles on it at present so maybe it will improve a little when fully run in.
In the GTI I could swap between Speed Limiter and Adaptive Cruise control from a button on the steering wheel, whereas now on the Tiguan it seems I have to go into the assistance systems (by pressing the button at the end of the indicator stalk) every time I want to change which is a pain.
Whilst the digital dash on the Tiguan does more than the GTI (i.e., much more configurable), it just doesn't look as nice as the Gen 1 AID's in the GTI.