To many of them to make a poll :)

I got my information from Wiki Endless Space 2  https://wiki.endless-space.com/academy

My favorite has to be Daro St Taiage.  Doesn't matter what faction I play, if I see I can recruit her, I don't hesitate.  I'll level her up as fast as I can on a new planet and get her onto one of my fleets asp.  She looks cool. great range with movement and she can hold her own in most battles.  Not to mention very good as a governor.

https://wiki.endless-space.com/academy/daro-st-taiage#identity

LORE: Daro was known as "The Burning Brand" for her eager and relentless proselytization of minor peoples. Ever eager to bring additional souls into the fold and to free spirits from their physical prisons, the Fount upon her Ark never lacked for sacrifices. Her worldview changed one day, however, while rounding up recalcitrant Kalgeros who were hiding in an Endless temple. Touched by the presence of the Virtual Endless who called itself Taiage, Daro came face-to-face and soul-to-soul with one of her gods. The reality of this knowledge shocked and altered her profoundly. Still driven to serve a God, and yet sharing her Cloth with its presence, Daro now alternates between burning with faith and aggression and fearing what ultimate sacrifice her symbiotic Saint may require of her. What is the recompense for sacrifice? What is the ultimate act of fidelity? It is one thing to act as if believing your god follows your every movement and thought; it is quite another thing to live that way.

Also she is vodyani, so a must have for the ridiculous FIDSI per level bonus while being militaristic makes her easy to keep her place in senate for the bonus to apply.

Only shame is, that she isn't a guardian. Guardian op.

My fav is Vodyani starter.

1) you are guaranteed to have him as vodyani (so basically a faction bonus)

2) OP AF and can carry the game singlehandedly with vodyani and guardian skills

3) vodyani tricks enable you to throw him around a lot within a single turn and minimize his downtime if things don't go well

4) gets +10 influence on system as bonus, which is nice to have in early game

5) is religious and practically never gets kicked out of the senate