I bought a i20 Asta automatic transmission as I have knee problems. At first I was apprehensive about AT but having now driven a AF car for over 15000 kms I am all for AT. It makes driving in Mumbai traffic such a pleasure.
Now about mileage:
Highway: 14 kms/litre
City: 11 kms/litre
Mixed: 13 kms/litre
That is with a petrol i20 AT. I don’t think other manual cars 1400 cc give any better mileage. And even if it gives me less it is OK s it is kind on my knees and heart (less stress).