Hi! This guide is for beginners or people who want to try to play Atlantica. Although there are lots of character guides out there, I would like to share it here.
Sword: A sword main is primarily a tank in your formation. He has decent HP and very good defense. Swords will save you one space at the back and middle formation for a magician or archer. Together with a monk (either protect or shield of protection passive ability), your sword will be a very tough nut to crack. In free and colo leagues, your characters at the back of your main will most likely survive (unless they are sniped by ranged units) since your main is probably the best and strongest front liner.
Spear: Spear main can serve as a tank, but not as good as sword. If you really need to put him in front, be ready to occasionally switch him with another mercenary. Spears are good in terms of attacking the action power of enemies. Mixed with another spearman, you can significantly reduce the action power of the entire column and prevent them from attacking.
Axe: Axe mains are good melee damage dealers. Their attacks are strong and damage a row of enemies. They also have a very good skill which can freeze an entire row of enemies. The only downside is that their action power recovery is slow. Some people use another axe mercenary (viking) since he also has a freezing skill.
Bow: Bows are one of the major damage dealers of the game. They have good multi-hit rate and they can attack anyone in the enemy's formation. Bow mains are usually used in tandem with other ranged units to snipe low defense, high functionality mercs behind your front line like monks, healers, and prophets.
Gun: Gunner mains boast their basic attack which hit the entire column of enemies. The advantage of this is that it is difficult for your enemy to heal his mercs since healing abilities affect rows, not columns. Gun mains are also good in stun builds since they hit three mercs at a time.
Cannon: Cannon mains do AOE damage so it obviously is not good for spike builds. They damage enemies in a t-shape area so he can hit up to 5 enemies when you target the middle. Cannon mains are usually used for stun builds since they can attack anyone from the enemy's formation and they hit a lot of mercenaries.
Staff: Staff mains do two things, either use strong AOE magic against enemies or provide support to your characters like healing. He has very good magic defense so he/she can withstand magic damage, especially AOE magics which hit everyone in your formation.
Instrument: Instrument mains have good AOE magics. They not only do relatively decent damage, but they weaken all of your opponents as well. Their debuff skills are usually used as early as possible to weaken enemies.
Powersaw: Many people believe that powersaw mains are overpowered. First of all, powersaw is not available unless you already have another character who reached level 100. Now, there are many reasons why people say they are overpowered. First is that they have very good attacks. Their basic attack is strong and hits a row of enemies. They also have strong (wait, strong is a weak word for it), they have devastating AOE skills, one of which hits the entire row, while the other hits everyone. Not only that, powersaw also have good defense. Some people put them in front since they can withstand a lot of damage. Because of these reasons, many people make powersaw alternates once they have a level 100 character.
That would be it! I hope you find this guide helpful.