Most powerful affirmations?

[Rasheed]

 Which affirmations are the most powerful?

[Waken]

I'm a bit of a Conversations with God book nut. In those books it's explained that affirmations don't really work well when you don't believe in them. Take something you do or can believe and affirm that.

For instance if you're in a rut, don't say "I'm in excellent health" because your mind knows that's a lie. Instead you might feel the following is true, which would work better: "I'm becoming healthier every day"