Town. Its buildings can maximize the output of one measly grain. The high materials means that you'll build those food-boosting improvements fast. Getting the town past lvl 3 will be hard (many other towns with butchers can overcome the 1 grain), but choose "guild warehouse" at level 3 and set the queue to produce wealth and it'll help boost your economy. Also, you'll quickly be able to build the grocer and then up to butcher, which really helps your overall faction.

I use those for Fortresses and Conclaves and the 3,4 and 5 grain cities for Towns.  Works great for me, but I can understand why people would develop them differently.

you won't grow a 1-grain city to level 5 because you'll need >20 butchers across your empire (when you have them, who cares about a single city anymore?) and you'll need >10 to get to level 4, so you're basically stuck with a level 3 city.

A level 3 fortress with zero essences is useless to me, you miss the city enchantements for unit training and the production bonus coming with the lvl4 and lvl5 (a lvl 5 conclave with 4 essences and alchemist lab is usually the highest production city, the one dedicated to expensive building) - what purpose should it have? Pioneer training? On the other hand if it has 2+ essences it can be useful to train backup units.

A lvl 3 town will generate enough gildar only with 3+ essences and the propaganda spell; less than that the city suffers from the lack of the higher level bonuses (you can have some +% modifers but the base value is too low); it can however be used for the faction-wide food bonus provided by the grocer line of buildings (it isn't tied to the level of the city).

A lvl 3 conclave can produce some research but it can shine only with essences because of the herbalist line of buildings; a high material high essence conclave is the best producing city of the game thanks to arcane forge and alchemist lab, no matter the grain.

So my advice is: 0-1 essence, build a town or salt the land; 2+ essences, build a conclave (you will gain an additional essence with the oracle upgrade at lvl 3) or, if you really need it, a backup fortress.

with alot of cities and the food production tech researched you can grow any city to level 5, but maybe you're already winning at that point.

A 1-grain fortress/conclave (no well/festival), without access to a river (pretty common) needs 27 butchers to get to level 5 (26 if Empire). If it has 1 essence available for the nature's bounty spell (native essence, oracle upgrade, scrying pool as you said) - 2 grain total - it still needs 23 butchers to get lvl 5 (8 to level 4). The key here is the number of essences, to raise the efficiency of the Gentle Rain enchantment or, even better, the access to the wild grain resource (+1/2 grain). When a city reach 4 grain it can get to level 5 easily; less than that it has to struggle and it's difficult to achieve in standard maps. I like to have high level cities fast and that's why I usually settle in 3+ grain tiles, unless I find a tile with 3 or 4 essences (rare but more valuable than anything else).

Great info. I think my cities grows a bit slowly and was thinking of settling on some bad tiles without any essence on them. Now I know that those essence-less tiles better have good grain /and material/ or it won't be useful.