Set the budget first, so that you end up with a fair comparison and not like many buyer start from 50k and then end up buying 90k car.
Tiguan is compact SUV vs Touareg, so space wise Touareg wins.
If daily kms fuel usage is not of big concern for you, I would suggest Touareg any day, being proven through the test of time unlike Tiguan or any other recent release.
Also, Touareg is a VW flagship model, so chances of cheap material or timed spare parts will be far less.
Last but not least, whichever option you buy, make sure its well serviced and if its with full dealer service history then its worth more in its value, so you can buy at premium (worth it). German cars are good for first 5 years in GCC, then next 5 years are totally dependent on how well they were taken care previously (not forgiving like Japanese and US marque).