Rangers
The first unit in the game. They are very cheap and effective, and can deal decent damage to a single zombie or horde. They are currently the fastest unit in the game (4 tiles per second), making them great for scouting or escaping zombies. At the same time, if they are not protected behind the walls during the wave, they will quickly die.
Soldiers
They are very tough and powerful, but to create them you need to mine iron, not wood, which can be a big problem. But cost issues aside, these guys are great for battling waves of zombies or harpies. Soldiers have twice the health of Rangers; better armor, twice the attack speed, they do more damage, but at the same time, they have less movement speed and attack range than rangers.
Snipers
Snipers are slow to move and attack, but have more damage and range than almost any other unit in the game. To research them, you need a large amount of gold (wooden workshop), and to produce them, you will need wood and iron. These guys are great at destroying Dead Villages, and if they have cover they can clear the map well early on.
Thanatos
In my opinion, Thanatos are the worst type of late unit in the game, except for the final wave, during which they are insanely good. Oil and gold are needed for their production and research. Thanatos do almost the same damage as snipers. Just hire a lot of these guys to tackle the final wave and enjoy the show.
Lucifers
Lucifers are good enough for hordes of almost all waves, except for the final one, where Thanatos enter the battle. Basically, they don't need research, they don't need a lot of resources to create, and they can easily deal with the horde. But there are also disadvantages: firstly, these guys cannot attack through walls, and secondly, they cannot fight next to other units except Lucifers, because their flame can damage other units and ultimately kill them.
Titans
The Titan deals an insane amount of damage and has the same attack speed, in connection with which it can rival the damage of the sniper and the attack speed of the soldier. He has a huge amount of health and armor, and can also rival the ranger in terms of movement speed and even attack radius. It takes a huge amount of resources to create titans, but it's all worth it, trust me.
