Unmodified highest Speed stat will gain Priority (i.e. excluding buff/debuffs). Some Creature abilities allow the opponent to gain Priority despite having the lower Speed stat.
 
Speed ties are resolved as follows: 
  • If Creatures have the same Speed, the Creature with the higher Level gains Priority.
  • If Creatures have the same Speed and Level, the higher Rarity gains Priority.
  • If Creatures have the same Speed, Level and Rarity, the player that chooses an Ability first will gain Priority.