Cultus- CNG efficent, comfortable, more leg room then the other mentioned cars, mantainance is cheap and spares are easily available.
Cuore- Fuel efficency is good, leg room is lesser, mantainance is not that cheap if compared with Cultus, spares are available at Toyota dealerships and at local market.
Chevrolet Spark- None of my aquintances own one so cannot tell you about it.