to choose a char depends on how you want to play.
you have:
int priest (you give point to int to wield the best armor) if you are buffer/healer or healer/rezzer rezzer/healer You don't have to attack but only buff and heal and debuff creatures. (i woud'nt reccomand a rezzer/buffer it is better to find a buffer that can give you some good buffs.)
rouge:archer you can easy kill monsters with a higher lvl then you by shooting and running away. you do great ranged dammage but your hp is kind of low.
rouge:assasin: you can easly do one hit ko by using spike (thrust and pierce for lower lvl's. this is realy helpfull to kill orcs who have low hp. you better can get enough hp points to get wield best possible armour for your lvl and the rest to dex.
Mage: you can easly kill multiple creatures if you use aeo. but if you attack multiple creatures and can't kill them fast enough they will all will attack you and you will die soon.
warrior: you do normal~high dammage and you can stay allive long. you don't die fast but realy need a good weapon.
hope this all helped and sorry for the spelling mistakes