Great question! The priest class is unique, in that from a lore perspective, it focuses on the beliefs of that race’s religion or philosophy. I will give a brief explanation on a few of the iconic organizations with the WarCraft setting.
Church of the Holy Light
Racial Members: Humans and Dwarves of the Alliance
“It was the race of humanity who first discovered the magic known as the Holy Light within Azeroth and spread its teachings to their allies, the high elves and dwarves of the Alliance. The majority of this faith are the various human kingdoms such as Lordaeron and Stormwind. Unlike arcane magic which takes study and practice, the difference is that The Holy Light is a philosophy based on one’s belief in what they are doing. Its signature ability is the power to heal both body and mind. Alonsus Foal, being one of the most instrumental Archbishops, who served the Alliance during the First and Second Wars against the Horde. A cleric will focus on giving sermons to inspire and bless. Their main obligation being to heal the sick or wounded. While inquisitor’s call down holy fire against the undead and demons alike. Character archetypes could be from the caring, pious or inquisitor.”
Cult of the Forgotten Shadows
Racial Members: The Undead Forsaken and Human Cultists
“It was the human priestess Seline who dabbled into the mysterious philosophy of the shadows. Feeling that the human nations needed more power to take on the mighty orcish Hordes during the early Wars. She abruptly disappeared before she could spread her teachings on a larger scale but her dark findings were found by the Undead Forsaken within the ruins of the once great kingdom of Lordaeron. The Forsaken took immediately to its teachings and the dark clerics were born. As Light can heal the mind and soul, shadow does the exact opposite. It is a terrifying magic and also can have its consequences on the user. The forsaken being undead, this form of dark magic actually helps them such as using spells like shadow mending, where the Holy Light hurts them. Character archetypes would be those who feel abandoned by the Holy Light, or led to its teachings by mysterious whispers of ancient void beings. In the end vengeance is your aim and fealty to the dark Gods is your obligation.”
Sisterhood of Elune
Racial Members: Night Elves
“The Night Elves are one of my favorite priest races. Where humanity follows a philosophy, the Night Elven Priestess’ actually have a religion. For thousands of years the Night Elven people have followed their Moon Goddess Elune. They have a connection to the animal kingdoms and work in tandem with the Druid council. Many priestesses have deep connection to their saber mounts and the two act as one within combat. Elune’s radiant astral power can be used to heal their comrades or harm their enemies. A priestess may also access the Night Warrior’s power of Elune to exact terrible shadow magic upon her enemies. A priestess is elegant in her poise, and undaunted in her cause. Her faith is as the shining of the full moon and her wrath as terrible as the darkest night.”
Aldor
Racial Members: Draenei
“Eons ago, the fallen Titan Lord Sargeras offered the Eredar race a promise of unlimited power through the chaotic magic known as Fel. Two of their great monarch’s accepted, however, the last monarch Velen did not. He had been given a vision by equally powerful beings known as the Naaru beings of pure Holy Light. As the horror’s of the chaotic demonic magic began to unravel their very world the Naaru came to the Eredar’s people’s aid who had chosen the peace of the Light instead of darkness. Eredar fled their now dying homeworld on their dimensional traveling fortress called the Exodar. They renamed themselves Draenei which meant “exiled ones.” On board their realm traveling fortress the Draenei were taught the ways of the Light and overtime they developed a special gift from the Naaru. Priests in the Draenei culture are called Anchorites. The group of the Aldor was formed and Velen appointed one of its most devoted followers Ishanah as the organization’s leader.”
Unfortunately I wasn’t able to cover all the various cultures and organizations. In the end choose what you feel is the most epic!