Interesting Question: Glad you asked ...
Of the choices you offered (all adding up to 8), I think 3 grain, 3 production, 2 essence is usually best. Most of the time a balanced start is best, because you really do not know (beyond a very small area) what you will encounter. As Cauldyth suggested (in this magic-oriented game) essence is the most critically important thing in your first city. Production is second, and grain is third.
It DOES drive me crazy, not to have my first city be the biggest city, and a fitting Capital City; so I really wish my first city could always have at least 4 grain, or even 5. But in the short to middle term of the game, growth and population can take a relative back seat to magic and production, at least in your FIRST settlement.
By the way, as a practical matter, I usually settle a 4,3,2 (adds up to 9, of course) for my first city ... I generally won't "settle" for less ...