This is my opinion on a manual compared to an auto simply for the following reasons,
Driver used to manual (they drive the auto like a manual, they want quick pickup)
Tourism involves hill country travel - higher fuel+brake pad cost
Practically difficult to change sri lankan spoiled drivers driving style.(My personal exp)
Less engine wearing on manual transmission (as auto involves higher rpms to accelerate)
Higher rpm leads to higher fuel cost
Dual A/C requires more pulling power.
But as clearly said SuperGL will not have manual transmission. Passenger comfort wise auto is much better as well.
On average we get 6 - 7 km/l with KDH200 (2500cc) auto model with dual A/C.
Also note that you have to use Super Diesel for these models, otherwise so much trouble in the long run.
Good luck with your decision.