Haphazard

The most appropriate antonym of the word "haphazard" is orderly.

• Haphazard means "without any plan or method; random."
• Orderly means "arranged in a systematic or methodical way."

The other words do not have the same meaning as "haphazard" and are therefore not antonyms.

• Accidental means "happening by chance."
• Sporadic means "occurring at irregular intervals or only in isolated cases."
• Amazing means "causing great surprise or wonder; astonishing."