* Careless
* Sloppy
* Negligent
* Inattentive
* Haphazard
* Perfunctory
* Casual
* Lackadaisical
* Superficial
* Slipshod
The best antonym will depend on the specific context. For example, "careless" might be a good antonym if you're talking about someone's attention to detail, while "superficial" might be better if you're talking about someone's approach to a task.