If "wicked" means evil or morally bad:
* Good
* Virtuous
* Decent
* Kind
* Benevolent
* Just
If "wicked" means very good or enjoyable:
* Boring
* Dull
* Mediocre
* Unremarkable
If "wicked" means mischievous or playful:
* Serious
* Sober
* Formal
* Proper
To choose the best antonym, consider the specific meaning of "wicked" in the sentence you are using it in.