Formal:
* Je suis magnifique. (This is the most literal translation, but it can sound a bit dramatic or self-important.)
* Je suis extraordinaire. (This means "I am extraordinary," implying a sense of greatness.)
* Je suis remarquable. (This means "I am remarkable," highlighting your uniqueness and special qualities.)
Informal:
* Je suis génial(e). (This means "I am awesome," a more casual and playful way to say you are great.)
* Je suis super. (This means "I am super," another casual way to express a positive self-image.)
The best way to say it depends on the context and who you're talking to.