General:
* Communication skills
* Composition skills
* Literary skills
* Expression skills
* Penmanship (for handwriting)
* Wordcraft
* Articulation
More specific:
* Storytelling ability
* Persuasive writing ability
* Technical writing ability
* Copywriting skills
* Journalistic skills
* Editing skills
Informal:
* Fluent writing
* Strong pen
* Gift for words
* Wordsmith
The best choice depends on the specific situation and what you're trying to communicate.