Done a lot of research on liva, figo, swift diesel but finally stood with figo diesel titanium, completed only 150 kms, Got 12kmpl in city(Bangalore)with AC on all the time.Every car has its own drawbacks swift is quite expensive with less boot space, less features and more waiting time, Polo maintenance and service makes to think, no problem if you are a permanent resident in any city, Etios liva has a less boot space and even the service centers are less.
Finally I think that mileage is not only the factor to consider, If it is. then etios and swift are good options, but do keep in mind about the extra money spending when compared with figo diesel. Even those cars will not deliver the promised mileages in worst traffic conditions. Figo is an average car.