Classes are picked at the moment of character creation. You are given one Stone of Change free, but further changes require you to purchase more at 125 diamonds each. The class you pick will significantly affect your experience in the world of GearQuest.
Specializations: Counter Tactics, Damage Dealing, Opportunity
Rogues are regarded as the best class for PvP, due to Damage Dealing and Opportunity.
Specializations: Healing, Damage Dealing, Resistance
Titans are regarded as a good mix between PvP and PvE. While without the burst potential of Opportunity, they are able to heal themselves, and act as a good damage absorber via Resistance.
Specializations: Healing, Trading, Opportunity
Traders are also regarded as a good hybrid class, similarly to Titan, although they are more oriented towards the PvP side of things. They are able to deal good burst damage through Opportunity, as well as heal themselves in PvE.
Specializations: Healing, Counter Tactics, Resistance
Clerics are regarded as the best class for PvE, due to their complete immunity to PvP. Unless you have attacked somebody, or healed somebody PvP-active within the last 24 hours, you cannot be targeted by PvPers and your name will not be displayed in the Fight list. Clerics also have the all-important healing spell, which greatly increases their efficiency in PvE combat.
Note that you cannot start out as a Cleric, but have to use your free Stone of Change to do so. Also, immunity to PvP does not begin until one week after your class change.
Specializations: Damage Dealing, Counter Tactics, Resistance
Warriors are somewhat of a misnomer, as they are currently regarded as the worst class in both PvE and PvP. Lacking the burst potential of Opportunity, they are also unable to heal themselves. There is little a Warrior can do that another class cannot do better at. If you are looking to make the fullest out of your GQ experience, it is highly recommended that you give this class a miss.