660cc carb version was used in old model of alto back in 1980s ... and 660cc efi is new 1
for sure efi 1 is better
millage in manual will be great as auto drinks more , and on top of that all auto gear which comes in 660cc are 3 speed
only if you find engine from pino/carel they have 4 speed
on the other hand manual has 5 speed gear box and 16 to 19km/L is easy task in daily drive
and these engines are cheaper then 800cc carburetor engines