go for wagon r with eyes closed.
DO NOT BUY USED CAR FROM BANK, i repeat DO NOT BUY USED CAR FROM BANK.
you will be using car from bank for atleast 3-5 years. so get a new car
never install CNG in your car. NEVER.
i have 2011 1000cc Alto on petrol cng never installed and i still get 15 km/l on it inside City.
CNG will kill the car and people think cng car gives more mileage but new car gives double mileage on petrol thn cng.