I suggest you to test drive new Toyota Corolla before making the purchaase. It's an excellent VFM car. Mileage depends on certain parameters like how you drive the car, maintenance of the car, driving conditions, roads etc. More or less the mileage of both the 1.4 and 1.8 will be the same and don't expect mileage to be more than 10 kmpl. However, go for DSG automatic for the technology it offers and the driving comfort. Please remember that maintaining a Skoda and selling it in second hand market is still a big challenge.
Hope it helps!