well i would disagree
cuz it does not matter how you drive a car... the thing that matters is that the car is properly tuned and then the car is properly tuned to your style of driving
and when i say tuning i am not limiting to CNG kit tuning, i mean the over car.
We are running a Daewoo, its EFI and its tuned to consume more fuel and give out a good pick and speed...
I have also used corollas for a lot time, corroborator based, they worked well as well, the difference is changing from Petrol and back to CNG. In EFI its hassle free, in corroborator you have to keep in mind the fact of burning all the fuel in it before letting the CNG into the engine
I have driven VTi as well on CNG and its response time is also good.
So now the question of which cars are the best come down to one single factor the price category. So i would recommend telling about what category are you looking at in your mind and then going for the best in that category.