If "speechless" means unable to speak due to shock or awe:
* Articulate
* Talkative
* Loquacious
* Verbal
* Expressive
If "speechless" means lacking words or unable to express oneself:
* Eloquent
* Fluent
* Communicative
* Articulate
* Expressive
If "speechless" means silent or quiet:
* Loud
* Vocal
* Chatty
* Talkative
* Noisy
The best antonym will depend on the specific situation and the meaning you want to convey.