Forget CNG, you will only spend a lot of time in the long ques, and I hate the filling pressure of 3000 psi
CNG Cylinder weighs around 60 KGs, which is a lot of dead weight.
Go for LPG. Expensive if you compare it with CNG but cheaper than petrol, and obviously low pressure 200 psi
LPG Cylinders weighs only 12 KGs