One word substitute is Optimist.Sycophant: a person who acts obsequiously towards someone important in order to gain advantage.Optimist: a person who tends to be hopeful and confident about the future or the success of something.Cynic: a person who believes that people are motivated purely by self-interest rather than acting for honourable or unselfish reasons.Pessimist: a person who tends to see the worst aspect of things or believe that the worst will happen.