Agrarian Idyll & Inward Perfection are hyper-Unity civics, albeit the one had Pacifism+farms as requirement, the other Pacifism+Xenophobe.
And since you cap out on Unity quickly anyways, neither is technically needed.
Machinist turns out to be REALLY powerful, because it gurantuees you can pick Cyber-Ascension as soon as you unlock the 2nd perk slot (which, analogue to above, can be REALLY soon). As well, very high mineral output and early expansion rate, as long as you manage your energy wisely.
Parlamentary System is absurdly powerful with an easy to achieve and maintain +10/Influence per month. It only ever 'broke down' to 3 Influence per month (which is still very solid) after I spammed Frontier Outposts and ran into a bug permanently making all my factions unhappy (btw, this (can?) happen(s) whenever you embrace a faction, giving permanent happyness penalities).
Past that, picking the Architecture perk as starter is very useful, as it makes your early-game growth easier, and you can switch it out later for something more long-term-y.
Stacking Nationalistic Zeal with Xenophobe can give a pretty solid border push (and bonus rivalries for Influence), and is probably a default pick for Fanatic Purifiers, albeit you can easily gain 45% border extrusion by Supremacy Starter + Ascension Perk anyways.