Dungeon World

Officially, the druid is my favorit. The versatility of their shapeshifting and how it is tied into a specific kind of place gives it such a nice flavour.

Unofficially, it is the Mixed Adventure hack for the wizard. It removes the spell lists and instead uses a school/sphere system. The player describes the effect they want to achieve with the spell, but the effect must fit within the school their character has learned.