So Poster here is my review as per my best knowledge:-
JDM 660cc Car:
1. Better than Mehran in terms of performance.
2. Not much compatible with CNG (It will give issues if you install CNG). It will remain costly than CNG even if it does 25km/liter (ideally)
3. Availability of part may be hard, as you need to find in Junk Yard. So no new parts, you will find Kabuli/old parts from other accidented cars
4. If your car model is rare or newer then it will be very difficult to find spare part and if by luck you find it then it will be highly costly.
5. It is sophisticated car with Auto tranny, so not every mechanic would be able to handle it. You need to go to some good experienced mechanics which means heavy on pocket
6. No dealership, means no guarantee If something goes wrong or if you get defected car then you won't be able to complain anyone
1. Excellent car for traveling in city also if its your first ever car.
2. Parts are very easily available and very very economical.
3. Cheaper then 660cc because of CNG. (do the calculation of doing 100 kms on CNG and Petrol)
4. New Mehran comes with Warranty of 2 years. So it means peace of mind, if anything goes wrong then you can easily claim its warranty and it will be replaced for FREE.
5. Proper Dealership: If any tuning issue or minor CNG setting is needed then dealership will do it free in warranty period.
6. Due to simpler engine, every mechanic can easily work over it and you will also understand then engine basics.
7. Mehran is just like investment, it will never loss you (if maintained properly). Since you are looking for resale factor so you can't get any further butter option than Mehran. The cuore has been discontinued and Alto is soon going to discontinue. So you can think the resale factor of Mehran in near Future You would be able to resale is on your demand.
If its your first car so I would recommend Mehran, it will be in warranty and give you peace of mind. And once you get the know-how of car basics and maintenance then you can switch to some JDM (on your own risk )
Hope I answer you question!