There are currently 6 classes in Field Of Battle you should probably know them 

1.Fighter- Most people confer it to as the free class adds 20% sword dmg -20% sword cooldown and +5% to armor.

2.Mage -Class that gives you 400 mana points and 65% less mana cooldown and also adds 1 additional mana regeneration -85% to armor - 85% to melee dmg.

3.Archer - (Not Very Familiar with this class) Less bow cooldown and no run speed penalty with a bow and 65% more accuracy some penalty to armor and melee dmg. Also some penalty to mana.

4.Guardian - 200% to armor when near own general +60% melee dmg when near own general

5.Assassin- +50% more walkspeed +120% of melee dmg when behind target minus 50% to armor -30% to mana

6.Barbarian- + 40% more axe damage  -55% axe cooldown -50% to max mana

Fighter is the most balanced class for it has no penalties to any type of armor damage etc.