General opposites:
* Always: This implies something happens every time, in contrast to "usually" which implies it happens most of the time.
* Never: This implies something never happens, the opposite of "usually."
* Rarely: This implies something happens infrequently, the opposite of "usually" happening often.
* Seldom: Similar to "rarely," this suggests something doesn't happen often.
Contextual opposites:
* Occasionally: This implies something happens from time to time, but not regularly.
* Sometimes: Similar to "occasionally," this suggests something happens on some occasions, but not always.
* Infrequently: This implies something happens very rarely.
The best antonym depends on the specific context and the nuance you want to convey.