PROS:
I have bought Spark LS in 2010. Car is good in driving, low vibration & engine noice. Car looks small from outside but when you sit inside it feel great as compare to Alto or Wagon R. It is little smaller than Santro in size from inside. I think If someone want to buy santro its best to go for spark. It easy to take sharp turn & parking this car is too easy. Car has tubeless tyre & I think in this category no one offering this.
CONS:
I ran this car 10K in petrol. Without AC car is ok but when AC on its hard to pick-up. Also AC is not very effective . Fuel average is also low . I got 14 without AC in city driving condition. Gears are also too hard to shift mainly 2nd & back. As 90% mentioned in their review about front grill it make hard driving when you have to take turn right.
CNG PROS:
After spending too much on petrol I fitted CNG (BRC Kit) kit in car. It is close loop system. Rs.30K with RC endorsement. Car is running good in CNG without AC. No difference in pick-up & speed as compre to petrol. Running cost also comes down. It giving around 21 - 22 KM average without AC. I have 12 kg cylinder which can store maximum 10 KG CNG. All you have to do is to change Air Filter & Spark Plug after 10K running. I have no problem in CNG & happy to install.
CNG CONS :
As I mentioned, no pickup difference without AC but when AC on it makes difference. So if you have installed ADVANCER it will give you some relief. Cylinder weight is around 80Kg, it means when 4 persons is travelling actually they are 5. So its better if only 4 people travel in CNG spark. As every one knows loss of boot space in CNG installation so here we have to compromise with boot space.
CONCLUSION:
Spark is better in CNG (more average, less fuel expense) if you dont mind to give up you dicky space.