The following statistics are the base ones you can modify most easily with soul stones or rings in Rappelz.
Strength
Adds 2 Physical Attack when wielding a melee weapon and 3/8 Physical Attack when wielding a ranged weapon.
Great for physical direct damage dealers (usually those who wear warrior armor
or summoner classes)
Vitality
Adds 2 Physical Defense and 30 maximum Hit Points.
Basically required for tanks and great for all classes who take damage. If you solo a lot and take lots of hits, vitality is very good to socket your gear with. Also due to increasing maximum hit points, it slightly increases the amount of hp you regenerate per minute.
Agility
Adds 1/2 Evasion.
Not a very good statistic unless you want to have the best damage reduction, in which one should go half agility and half vitality stones. At low level for melee striders and assassins, agility is decent but vitality more consistently reduces damage taken and in many cases more damage total.
Intelligence
Adds 2 Magical Attack and 30 maximum Mana Points.
Great (almost necessary) for healers to have more maximum mana (and slightly more mana regen) and larger heals. Also great for more maximum mana and magical attack damage for dark magicians, kahunas (druids primarily), and other spell attack classes.
Wisdom
Adds 2 Magical Defense, 2/5 Magical Accuracy, and 1/2 Magical Resistance.
Not the best of all stats, but a small amount is decent for any spell attack class that attacks higher level monsters like in dungeons or farming solo or needs to crowd control monsters with spells. Probably the class that would need this statistic the most is the warlock. The magical defense and resistance is not very important, except in player vs. player.
Dexterity
Adds 13/8 Physical Attack when wielding a ranged weapon, 1/2 Accuracy (does not require ranged weapon), and 1/10 Magical Accuracy (does not require ranged weapon).
Dexterity is the best statistic for ranged characters such as archers and shadow hunters. I would highly suggest going half dexterity stones for a ranged physical character. Also a small amount of dexterity is good for physical damage dealers and pets who have problems missing monsters due to low base accuracy or higher level monsters.
Luck
Adds 1/5 Critical Ratio.
Luck is unavailable to get from soul stones, but Luck can be increased by rings. Since luck rings increase maximum mana points instead of health points, luck rings are generally only good for dark magicians (chaos magicians, warlocks). As one percent critical ratio only adds .8% total damage, in most cases it is better to have strength, dexterity, or intelligence (depending on your class) instead of luck.
