Azura. The main character is an Azura worshipper, and as I love Ashlanders...
The Nerevarine isn't necessarily an Azura worshipper.
Nerevar himself worshiped Azura but the Nerevarine is just a reincarnation, and the person is also from Cyrodill even if he/she is a Dark Elf. The person's religion is unknown and they can join either or both religious institutions in game as well as do tasks for Daedric Princes. They do a lot of Azura's dirty work but that's not the same as worshipping her outright.
Boethiah is my favorite of the three "Good Daedra" by the way, if for no other reason than he/she is the Warrior and the most honest and outwardly bloodthirsty of the three, not hiding behind poetry or mysticism like her brothers/sisters. Almalexia, the supposed champion of Boethiah, reflects this same personality very well during battle, being one of the most ferocious foes you'll face in the game.