IT`S A GAS

WHICH CAR?

Go for the Sonata. It is a bigger car than the Civic and is coming to you at a good price. What you save should go into fuel, which is not a bad thing.  As for CNG, get a conversion done at a good mechanic who is well-versed with the stuff, but do it after a year (after the warranty for the powertrain has expired). Once a good job is done, you don