Formal:
* Articulateness: Clearly and effectively expressing oneself.
* Fluency: The quality of speaking smoothly and easily.
* Graceful: Elegant and refined in style.
* Persuasiveness: Able to convince or influence others.
* Rhetoric: The art of speaking or writing effectively.
* Silver-tongued: Having a persuasive and charming way of speaking.
* Urbane: Sophisticated and polished in manner.
Informal:
* Well-spoken: Able to express oneself clearly and effectively.
* Glib: Smooth and easy in speech, often superficially persuasive.
* Articulate: Able to express oneself clearly and effectively.
* Fluent: Speaking smoothly and easily.
* Smooth-talking: Using charm or flattery to persuade.
Figurative:
* Golden-tongued: Having a very persuasive way of speaking.
* Silver-tongued: Having a persuasive and charming way of speaking.
* Sweet-talking: Using flattery to persuade.
The best synonym for "eloquence" depends on the specific context and the meaning you want to convey.