Races in WoW Classic provide much more meaningful bonuses to classes when compared their Retail counterparts. For the Priest class, both the Horde and Alliance have a specific race you should choose if you're looking to play one.
Strongest race for the Priest in WoW Classic
For the Alliance, Dwarves make the best Priest overall. This is almost entirely due to their two unique spells they get from leveling and questing.
- Fear Ward - Prevents the target affected by this spell from being feared. The buff lasts 10 minutes, and the spell has a 30-second cooldown. In Classic WoW (and Hardcore by extension), Fear is one of the most deadly spells to have cast upon you, as even a single cast of it can mean certain death for you.
- Desperate Prayer - Instantly heals the caster. Very nice for an emergency heal, but has a 10-second cooldown. This is a mini Lay-On-Hands spell specifically for Dwarf Priests.
Beyond these two spells, a Dwarf Priest also gets access to the fabled Stoneform, which grants immunity to Bleed, Poison, and Diseases. It additionally grants the Dwarf a 10% increase in armor. All of the mentioned effects last for eight seconds. For PvP, Stoneform is ridiculously useful for peeling pressure off yourself. In PvE, it has much more niche uses but can save your life against enemies that stack large amounts of poison effects very quickly.
For the Horde, Trolls make the best general Priests due to their two core racial abilities, although Undead does have access to one that makes this a choice if you're looking to deal DPS.
- Berserking - Boosts your cast speed by up to 30%. The lower your health, the better the cast speed buff from Berserking. Being able to cast faster means the Troll Priest can heal much more efficiently in emergencies. This racial alone puts the Troll race ahead of all others on the Horde side for a Priest.
- Regeneration - Trolls can passively regenerate their health during combat and outside of it. This is a direct increase in survivability, which is more than welcome in the Classic WoW game state (because death is a commonality there).
Undead Priests are an option solely for the added benefit of an extra DoT (Damage Over Time) spell through Devouring Plague. Devouring Plague is a nice extra source of damage for those players looking to play a Shadow Priest. If you are, then Undead is your best choice.
For more quality guides and useful information relating to World of Warcraft, check out Best Race for Mage in WoW Classic right here on Pro Game Guides.