Endless Space 2 has some pretty interesting and rather powerful Gameplay Affinities. Not to mention that some factions just feel a tad stronger than others if independent of what Gameplay Affinity they're tied to. In this thread feel free to list the one(s) that is(are) your favorite(s). For me, I have a top 3 on each.

Gameplay Affinities:

1) Gene Hunter. I think its safe to say that this is arguably the strongest Gameplay Affinity in the game. The ability to take your population and make it stronger over the course of any game, custom, or vanilla Horatio, is quite frankly broken as you can basically colonize any system once you Gene Splice those with +Happiness(Kalgeros and Kal'Tik'Ma being the most generous at +3 respectively). Those benefits translate into having 100% System and Empire Loyalty by the mid to late game, ensuring that you will have the upper hand in Food, Dust, Science and Influence output. Where this Gameplay Affinity shines the most is in a custom setup since you can take the OP Extreme Foremen perk and basically have it the entire game on top of all the +FIDS from Splicing other factions(which are then enhanced from Extreme Foremen).

2) Continuum Sculptors. After Gene Hunter, this Gameplay Affinity is number 2 for me. Although extremely tied to its native visual thanks to the changes to the Colony Base(and Colonization Tree), the ability to affect systems with a particular effect is quite powerful. Provided you get around the Food issue in a custom setup, this faction allows you to grab those tasty IDS rich Sterile planets ASAP. Add on the fact you start with extra Dust that allows you to refit your ships from the start.

3) Emperor's Will. Dust inflation is a huge problem in this game for me, hence why Lumeris' Planet Brokers didn't make my list. Yet the United Empire's Gameplay Affinity gets around that by giving players the means to tap into the Influence they generate each turn(immune to inflation) and I find that this is extremely potent Gameplay Ability that allows for multiple playstyles. The perk that really gets my attention is buying out research. This means that you'll always be relevant tech wise provided you make a determined effort at producing Influence. Arguably benefits the most from Tier 2 and 3 Influence Luxuries.

Visual Affinities:

1) United Empire. I may be biased on this one but let's admit that their perks are pretty nice. +1 Colonization Cap and 250/100 Manpower Modules at Tier 3 Military is hard to pass up. Add on Quest line perk of 10% Industry(for any custom faction or vanilla UE that chooses to remain as is), 10% Weapon Damage(Punisher Drives) and guarantee of 2 Imperial Heroes(both with Titan of Industry) leads to a solid choice. Did I happen to mention that their Medium and Carrier Hulls are some of the best?

2) Unfallen. This faction on an Emperor's Will setup is quite frankly broken. Their Heroes have 2 Influence perks that give gobs of Influence to go along with gobs of Food(making them perfect Governors). Their ships are tanky and their quest line can give some pretty nice buffs.

3) Horatio. Crazy to list them here seeing as I don't like their ships but they might be the ideal pairing for Continuum Sculptors Gameplay Affinity. They produce ample Food(including more to Manpower), solid Luxury Resource generation and have a unique perk of +1 cap on all planets on Compact Warp Methods Tech(meaning it applies to Neutral planets like Mediterranean, Steppes, Savannah, etc.). If you're looking for huge Lava Planets... yeah this might be the pick :)