My personal choice would be diesel. I got 13.8km/l in the 520d with some pretty hard driving, and 9.5km/l in the 730Ld with even harder driving. The Civic Hybrid returned 13.3km/l despite being driven sedately almost the entire time I had the car.
However, a note of caution is that our Euro 2M standard diesel still has pretty high sulphur content, and hence, whatever green promises held by diesels in Europe do not apply here.
Nevertheless, it should also be noted that our petrol is similarly unrefined. This gives the latest generation of direct injection engines from Europe a lot of problems. A good example is the upcoming F10 BMW 5-series, where the new 3.0-litre direct injection straight six engine will not be usable here for the time being.
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I guess the prob wt petrol engined FC claims are usually made based on relax/sedate driving at around 2,000-3,000 rpm which are ok if you are not in the hurry. In the real world, to extract power (bhp & Torque), most petrol engine need to be rev hard at 4,000-5,000rpm for quick acceleration/carry loads & ppl....hence, the claimed FC cannot be achieved. However, for diesel engined, the FC claims are made at the same driven rpm of btw 2,000 - 3,000rpm and its applies to the real world usage, as we all know....peak torque & power of a diesel engine are around that range. there no need to rev high to extract power from a diesel compared to a petrol, hence claims FC & real FC are ALMOST identical
Just my opinion...i'm no expert but based on experience of driving both type