The cleric has two sets of offensive powers - ranged powers based off of Wisdom, and melee powers based off of Strength. The defensive and otherwise tertiary powers are often based off of Charisma. The Wisdom-based powers are often known as "laser" powers due to the vast majority dealing radiant damage. A cleric prioritizes the stat which he uses for the bulk of his attack powers, with Charisma either secondary or tertiary depending on the mix. A single-build cleric will typically put 16s in either Wisdom and Charisma or Strength and Charisma, with the 12 used either in the third stat or for feat qualifications. A balanced cleric will instead put his 16s in Strength and Wisdom.
A Wisdom cleric makes a better healer and is generally in less need to use his healing on himself due to his range - he also has Sacred Flame, which can be extremely useful for the free saving throws it provides.
A Strength cleric is a better attacker, and has the best at-will cleric power in the game, Righteous Brand. However, he is generally in more danger than the Wisdom cleric.