Hmm , It's between Pyromancer and Warrior, I like Magic a lot, but I'm properly going to choose Warrior for my first play-through since the melee combat is the most challenging and fun, I'll eventually start the game all over again with new character and that would be either Pyromancer or Sorcerer.
I have no idea what the master key is .
---

Warrior – a fearless warrior and weapon expert with high strength, and dexterity.

Knight – a low-ranking knight with high HP and solid armor that is not easily toppled.

Wanderer – an aimless wanderer with high dexterity that wields a scimitar.

Thief - a guilt-ridden thief who deals high critical hits and has a Master Key.

Bandit – a savage bandit with high strength and wields a battle axe.

Hunter – a bow-wielding hunter who can handle close-range combat, but is vulnerable to magic.

Sorcerer – casts soul sorceries and from the Dragon School.

Pyromancer – casts fire spells and wields a hand axe.

Cleric – casts healing miracles and wields a mace.

Deprived – unclothed and starts the game with a club and old plank shield.

Source