The Temple Guardians (also known as Templars) guard the Temple, the largest gathering place for wizards in the world. They are best at being fast and aggressive, but they have options for every situation. Many of their cards get more powerful if their mana cap is an odd number.
The Thieves’ guild are a slow to medium speed, control oriented deck. Their faction ability allows them to steal enemy face-down cards if they can guess what they are.
The Mariners are a slow combo-based deck with extremely powerful Aquatic units that can only be used if the battlefield is flooded. You need specific cards to flood the battlefield, so you’ll have to manage your hand carefully. The Mariner faction ability, which lets you draw 3 cards and put 3 back instead of your normal draw, can help you do that.
The Fae are a fast combo-based deck with an unusual faction ability: They can keep one card face-down at the start of each of their turns. They also have Illusions, which have much more powerful effects than normal spells; but unlike normal spells, Illusions can be killed by units.