What kind of hair straightener is best?

I have wavy hair that is hard to control especially in humidity. My hairdresser uses a Paul Mitchell. My hair always stays straight, but I don't know if it's because of the straightener or mystery product she uses, or shampoo, or whatever variable it may be. I don't want to go drop tons of money for a straightener that doesn't work how I thought. So, girls, what straightener do you love that almost never fails?