Units are the purpose and driving force of the game. One simply cannot play without an effective army. This intends to guide you through the various types of units, and help you decide which is best.
First, are ground troops. They are the most common type, with various classes. They are easy to obtain most of the time, and are relatively inexpensive, depending on what they are exactly (i.e. a Soldier III is easier to get than a Space Viking Soldier, but more expensive than a Soldier II). Below, the classes will be described.
Worker - Cheap, and invaluable. Gather resources, but actually have some fighting capabilities in groups.
Soldiers - Cheap and fast. Constant, but weak, firepower. Strong in swarms.
Bazookas - Cheap, relatively slow. Provide knockback, and strong hits.
Melee - Close range. Somewhat expensive. High health and damage. Good in swarms, but expect high casualties and a lot of knockback.
Healers - Provide little combat application, but heal health to various units. Cheap, but relatively useless. Better to use a hospital and save your population for fighters.
Riders - Vehicle/Melee hybrid. Somewhat difficult to obtain.
Vehicles - Stronger and faster than bazookas and soldiers, yet more expensive. Jeeps are like soldiers, tanks like bazookas. Basically, just buffed soldiers and bazookas. Takes a lot of population.
Bots - Like mechs, but much weaker. Not difficult to obtain.
Dragons - Strong, rare, and expensive. Can spawn draggies.
Mechs - Strong, rare, expensive, and usually better than dragons. Can spawn drones. Both take large amounts of population.
Ground troops are good, but not without limitation. Being confined to ground, they are not very maneuverable, and must take long paths around walls while taking fire. This is where air troops come in handy. They fly over all buildings, and are able to get places much faster. Get them as soon as possible. Below is another list of air classes and capabilities.
Aircraft - Jets. They act pretty much as airborne bazookas. Cheap and powerful, they have knockback, but long delay.
Helicopters - Pretty much act as airborne soldiers. Cheap, somewhat weak, they are effective in groups.
Draggies - Baby dragons. They mainly shoot fireballs. For the most part, they are the stronger of air units. Difficult to obtain.
Drones - Small aircraft versions of mechs. Mainly shoot lasers, but are very effective. Difficult to obtain.
Though very effective, air units have two main weaknesses- Antiaircraft Batteries, and melee units. Antiaircraft batteries do massive damage to air units, and melee easily run down air units that fly straight to them.
Units are very important, but one's style is just as important. Develop your style, and keep only what you need and what you can use well.
Though aircraft are very good, they have two weaknesses- Antiaircraft batteries, and melee units. Antiaircraft units deal devastating damage to air units, and air units will practically fly into hordes of melee units that make quick work of planes a close range.
Strategy is the most important thing in Social Wars. If you don't know how to fight, you will lose more than you win. Swarming all units is a common tactic. Simple, yet effective, it focuses the firepower of your units while spreading the damage between units. Division is also used frequently, doing swarms of various types in waves. Best wave pattern is melee, bazooka, soldier, vehicle, air, and finally, mechs/dragons. The most effective I have seen is air strikes. They bypass walls and move swiftly. An even better version of this is drone strikes. Your mechs/dragons spawn drones, and they are sent in a swarm to attack. They can be infinitely respawned without consequence, and are formidable in great numbers. Always try to divert forces away from your target.