If "nevertheless" is used to introduce a contrasting idea:
* Therefore
* Consequently
* Hence
* So
* Accordingly
* Thus
* As a result
If "nevertheless" is used to emphasize a point despite a previous statement:
* However (can be used as both an antonym and a synonym depending on the context)
* Still
* Yet
* In spite of that
* Despite this
The best antonym will depend on the specific sentence and the nuance you want to convey.