To me it really depends on what I draw first in terms of square. The best square I could find was a 3 x 4 x 2, and bordered by a forest and a river. I could make anything there, it will have amazing production, but I went Fortress. My next city was a 3x3x3 on a river. That will be a perfect Conclave.
I really like my Fortress to be high production because getting your troops quickly is important. I am playing as Pariden so I can have 3 essence there for buffs.
If you are not Pariden, your first city, well, it depends, Conclaves are really better with essences, so if you don't have a 3 essence square, I would make a Town.