CNG is the better alternate for the cars. Go for factory fitted.

I brought it 6months back. I feel spacious and good mileage. Previously I had Wagon R Lpg. CNG is more fuel efficient than LPG. Toll prices are more when I travel from Bangalore to Hubli. Value for money. Great mileage of 34+kms/kg of CNG. 20+KMS/LTR of Petrol on highway(speed limited to 80-100). CNG station are coming up more and more. So no worries for the fuel pumps now. When I took in April very less stations were there. Now many have set up new stations. If thinking of space. Can go for Ertiga CNG.