I have driven Wagon R manual for over 2 years then switched to Cultus manual. Mostly driven within city.
Cultus gives a slightly better fuel average than Wagon R.
Wagon R Manual : 12.5 to 16.5 kmpl
Cultus Manual : 16.5 to 19.6 kmpl
I usually drive with a soft feet 90% of the time. The above average is with AC only. You can add another 1-1.5 kmpl without AC.