This is a quick look at stats and what they do in Raiderz. In Raiderz stats are the main component of determining the effectiveness of various skills since all of them multiply off of your base stats. Because of that it's important to know what they do.
STR: Strength increases physical damage.
AGI: Agility increases dodge and critical hit for both Magic and Physical Attack
INT: Magic damage and energy pool
VIT: Vitality is your health
CHA: Energy Regen is based on your charisma.
STA: Stamina points
Because of what each stats effect each class has a certain hierarchy of stats depending on what they are trying to accomplish.
Berserker: STR > AGI > STA >= VIT
Strength is most important on a Berserker since he is a damage dealer and all his skills multiply off it. Agility is second most important because it helps with crit which also aids in damage output. Personally, I put stamina and vitality as equals. Realistically you won't actually be trying to gear for either of those but will gain them passively.
Defender: VIT >= STR > AGI >= STA
Defenders are a strange class. Ideally you want to balance vitality and strength because you need to still do damage while soaking it, and generally you should be blocking most of the damage you have incoming. Stamina and agility are about as important as each other because Defender doesn't really need crit chance since he has a skill that will give 100% crit chance to the next skill anyway and has Stamina regen abilities.
Cleric: INT > CHA > AGI
Clerics really should be focusing purely on Int. Realistically it increases the potency of your heals and your mana pool which are the two things you want most. Although Charm will increase your EP regen, you have skills that do that. Agility is only if you're pushing for additional damage but Int still has more effect.
Sorcerer: INT > AGI > VIT
Sorcerers should be purely stacking INT when possible. Although Agility offers some nice crits, your overall damage will increase with INT. I only place vitality as an option since there are a lot of sorcerers that can be one shot. You should try to get just enough vitality that you can survive one shot from a boss, just in case.