Formal:
* Flawless: Perfect, without any flaws or defects.
* Faultless: Without fault or error.
* Exemplary: Serving as a model or example of excellence.
* Unsurpassable: Impossible to surpass or improve upon.
* Perfect: Without fault or imperfection.
* Immaculate: Perfectly clean and spotless.
* Spotless: Without a stain or blemish.
Informal:
* Top-notch: Of the highest quality.
* First-rate: Excellent.
* Outstanding: Exceptional.
* Superb: Excellent; magnificent.
* Brilliant: Exceptional in intelligence or ability.
Specific to certain contexts:
* Precise: Accurate and exact. (For details or work)
* Elegant: Graceful and stylish. (For appearance or style)
* Refined: Elegant and sophisticated. (For manners or taste)
* Crisp: Neat and tidy. (For appearance or presentation)
The best synonym will depend on the specific situation and the meaning you want to convey.