I have a manual 9th gen civic and trust me when I say this, its a beast if you know how to drive it
Economy wise its really good giving around 13/14 km/l in city on light foot and if you open the throttle then falls to 10 sometimes less. Compared to auto i think mileage is great and its wrong to say that auto can give more mileage i have tested a friends car thats auto. Also its a lot faster than automatic (kills any car on the road uptil now) because theres a gear ratio difference also the auto manual difference. If you like manual and dont want to kill the fun of a civic then go for manual best option. Other wise for normal driving auto is good too for more traffic or old people.