Do they exist? Do they entirely depend on map or map size/type?
Here's what I'm doing currently for my main land factory and usually for additionals (not one used only for engineer production):
T1 Land:
tank, aa, arty, tank, aa, arty, tank, arty, tank, arty
Sometimes, for the additional land factories, I omit the aa.
T2 Land AEON:
Usually go for blazes due to the front-end nature of obsidians early on, and shift from blazes to obsidians when opponent has t2.
Blaze x 3, aa, mml
then shifting to Obsidian x 3, aa, mml
T2 Land Seraphim:
Ilshy, Ilshy, Ilshy, aa, mml
T1 Air:
Interceptors almost exclusively
As for engineers, if I'm Seraphim, I try to use an air factory to produce engineers. Otherwise, I devote 1 land factory for engineers in an endless loop .
Please comment and critique, I'd appreciate pointers and suggestions.