Formal:
* Eu sou incrível. (Literally: I am incredible)
* Eu sou extraordinário/extraordinária. (Literally: I am extraordinary)
* Eu sou fantástico/fantástica. (Literally: I am fantastic)
Informal:
* Eu sou demais! (Literally: I am too much!)
* Eu sou incrível! (Literally: I am incredible)
* Eu sou demais! (Literally: I am too much!)
* Eu sou foda! (Literally: I am badass, but it's a bit vulgar)
Other options:
* Sou um gênio! (Literally: I am a genius!) - implies that you are intelligent or skilled.
* Sou único! (Literally: I am unique!) - emphasizes your distinctiveness.
The best choice depends on the situation. For example, you might use "Eu sou incrível" with friends and "Eu sou extraordinário/extraordinária" in a professional setting.