Affinity is commonly the most overlooked advancement tree initially in Beyond Earth that newcomers forget to pay attention to. Too often, the first thing most players are thinking about is what they are going to research, but they don't see how certain research techniques give them affinity.

Affinity is your sponsor and nation's political, societal, and technological directives, and it is how they relate to other nations as well. I am going to show you the strengths that each of these affinities has. It is hard to say which of these affinities is the best because they are all well balanced.

However, depending on your sponsor, there may be an affinity that's more advantageous and has symmetry with other powers to give you an advantage. Let's go over the affinities 1 by 1 and determine which affinity is meant for you.

Harmony

 Harmony is a directive towards harmonizing with the alien planet and changing humanity to adapt to it. It has units that specialize in the hybridization of human and alien combat. They heal in miasma and even anywhere faster and also have the ability to "leash" aliens and turn them into units under your explorers.

You still have technologies you need to research before you can get there, though, and there are perks they don't have. I think if you're going to focus on a harmony build, the African sponsor does great as there are buildings for food growth along the way for harmony. I definitely love the feeling of taming the alien atmosphere and getting all in love with the collective consciousness, but I leave it to you to decide if you need a Mind Flower to do it or not!

•  The end game for Harmony is definitely the easiest as it's a straightforward defense for a position for x amount of turns.

• Their strategic resource, Biomass, Gives your city extra food and eventually science at lvl 12 which is wayyy down the line.

• The best wonders along their affinity tree are just the Drone sphere, Gene Vault, and Nanothermite.

• They have along their affinity tree buildings that improve culture and health primarily.

• Awesome self healing units that get more healing in miasma!

   Choose Harmony if…

• You want faster growing culture and cities due to the buildings and strategic resource related to them

• You want to use Miasma in your battle strategy which is amazing for defense giving your enemies constant damage and your units strength boosts and healing boosts

• You want to amass a large alien army and leash potentially colossal aliens such as the worm and the kraken. Great for early game builds!

• If you want to focus early on building explorers and finding artifacts instead of killing aliens.

PurityPurity is the directive to maintain the course of the mission and bring settlers from planet Earth to the new planet that has been terraformed and prepared for them.

• They have some of the straightforward combat bonuses that don't require particular conditions and have great ranged units that can hover! Including their most powerful unit!
•  On the tech tree most of the military units can be found where you earn purity points. 
•  Their 1st unique infantry unit cost just titanium which makes it easy to pop a few of them battlesuits out no problem!
•  easier accessible technologies to progress in the respective affinity.  
• Best wonders along the affinity tree are Markov Eclipse and The Crawler
• Floatstone generates extra energy for your cities

 Choose Purity if…

• You want to focus on building your military and be offensive. They have great siege units! Plus getting most of the basic military units is on their affinity path!
• You want a challenge for their victory is the most challenging with having to bring settlers out from earth to settle cities
• You want to destroy aliens early in the game! You’ll have combat bonuses early on to destroy them. 
• You like Terrascapes and domes for these tile improvements come with extra perks

Supremacy

Supremacy is the directive to improve humanity through the breakthroughs in technology discovered on this journey. You are the soldiers of that new command whose plan is to bring the new future back to planet Earth. It's hard to tell how machine or human they are, but it must be working for them.

• They have a unique advantage of having orbital range wherever there is firaxite which makes the strategy of teleporting your army into the middle of their base pretty logistically possible. 
• Vertical farming, an incredible tech, is along one of there branches
• Titanium is along there affinity path and gives your cities an amazing production boost
• Firaxite gives a science boost to your cities
• Master Control, Guo Pu Yaolan, Precog Projects, and the Faraday Gyre are great wonders along there path

Choose Supremacy if…

• You want to find artifacts early on and improve your production and science output quickly
• You want Battleships that act as carriers one of my favorite units for Supremacy for it gives your fleet easy air offense/defense 
• You want a mixture of offense and defense for Supremacy has amazing ranged siege units which can protect just as easily as they destroy from afar.
• You like node improvements that heal nearby fighting units because they will give you extra energy.