These are the mercenaries that can do the most damage, they have "Favorite Target: Anything". These mercenaries will destroy every building close to them with ease. They don't have much health and can die easily if not properly protected. Only the Rock'n Gaul has high health and is able to take a lot of damage.
These mercenaries are very versatile, some have high movement speed some are slow. Persian Sappers can avoid damage and traps while being underground, Hezarfens are flying units and have ranged attacks. Beduoin Brutes are most effective in large numbers. Each mercenary type has its own unique thing and damage output.
The Longbowman Squad was introduced as the reward of the Head HuntersEvent, These Longbowman Squad also have "Favorite Target: Anything" unlike the normal mercenaries these are deployed in a group of 6, these are the first ground ranged mercenaries in the game.
In the 2014-08-04 update the Persian Sapper "Favorite Target" was changed from "Anything" to "Defensive Towers" and is no longer considered as a dps but as a tower destroyer.