General synonyms:
* Articulate: Able to express oneself clearly and effectively.
* Fluent: Speaking or writing easily and smoothly.
* Expressive: Communicating feelings or ideas clearly and effectively.
* Persuasive: Able to convince or influence others.
* Powerful: Having a strong effect on the listener or reader.
* Effective: Successful in producing a desired result.
More specific synonyms:
* Grandiloquent: Pompous or bombastic in language.
* Silver-tongued: Having a persuasive and charming way with words.
* Oratorical: Relating to public speaking.
* Poetic: Having the beauty and rhythm of poetry.
* Elegant: Graceful and refined in style.
* Witty: Clever and humorous.
* Lyrical: Expressive and musical in style.
Antonyms:
* Inarticulate: Unable to express oneself clearly.
* Mumbling: Speaking unclearly and indistinctly.
* Rambling: Speaking or writing in a confused or disorganized way.
* Vague: Not clearly expressed or understood.
* Unconvincing: Failing to persuade or convince.
The best word to use will depend on the specific context. Consider the speaker, the audience, and the message being conveyed.