Magical background

This background has the lowest hitpoints, but highest spellpoints. All magical background guilds are focused on blasting.

Mages

RoleBlaster, protter
DescriptionThe main damage-dealing and protting guild in the game. Party-only guild.
StructureThis guild is unique in that it consists of subguilds. First you complete the base guild that gives some starter spells, then you can join elemental guilds - each of these takes 10 levels and gives you blasts and protective spells for one damage type. Maxing out at least one elemental guild allows you to join the inner circle, which gives you various protective and support spells.
Important skillsCast X, masteries, Quick chant, Analysis of magic lore, Create staff
Important spellsMain blasts, Armour of aether, big elemental protective spells, Conjure element, Shelter
Rep/questsUsing the main blasts gives essence that improves damage and reduces sp costs. Blasting with the mage staff gradually gives it various bonuses.
Other considerationsMages are a party guild, they do not work well solo unless you also join the Riftwalkers guild. Mages also require a lot of experience to work reliably. Each elemental guild costs 33% more than the previous one, and you want to join at least three of these. At lower experience totals, channellers, or joining another background, may be a better choice.
More information

Riftwalkers

RoleMelee blaster
DescriptionThe main purpose of this guild is to allow magical background characters to do solo fighting. It allows summoning an entity that tanks instead of the player, and does melee damage too.
Important skillsEntity control, Rift energy flow, Mastery of rift entities
Important spellsSpark birth, Rift pulse, Create rift, Establish entity control, Summon rift entity, Regenerate rift entity, Heal self
Rep/questsEntities start very weak and need to be built up. Completing a series of tasks gives various bonuses.
Other considerationsThe guild has more micro-management than other guilds, as you need to coordinate attacks of your entity too. Using the entity can prevent non-riftwalker spells.
More information

Channellers

RoleBlaster, debuffer
DescriptionChannellers are similar to mages in that they are mainly focused on doing damage. Their spells are generally weaker than the mage ones, but they get channelling effects that let them drain sps, replenish allies, and such. They also get resistance-reducing spells, which are very useful against certain monsters.
Important skillsCast channelling, Mastery of channelling/draining, Flow of magic
Important spellsChannel* blasts, Energy aura, Energy vortex, Grounding point, Spontaneous combustion
Rep/questsGuild quests, golem tests
Other considerations 
More information

Psionicists

RoleBlaster, stunner
DescriptionBlasters with psionic spells, some utility, and stunning attacks. Their stunning attacks are useful in experience parties - although barbarians are preferred for this role.
Important skillsCast psionic, Theory of mental power, Knowledge of mental defence
Important spellsPsychic crush, Paralyze, Psychic purge, Mindseize
Rep/questsSeizing mobs' minds allows studying some extra spells. Some quests give stat bonuses.
More information