Great Generals for me, is almost always in a city unless its doing a some kind of defense or push some where else.
There's too much variable for me to simply pick one.
Plenty of cities near each other = foot infantry.
Wide open pasture and a river with bridge built = horse.
I almost never build ranged units. =/ But I've used practically everything as a garrison force, including giant death robots. XD
Depending on the terrain, you can literally get away with defending six cities with nothing but one melee unit and a great general against superior numbers. While the rest of your army is fighting against someone else nerd raging on you.