He is a good fellow; but what I dislike is his reckless handling of things.

Answer: Option B

Reckless : heedless of danger or the consequences of one's actions; rash or impetuous.
Intelligent : having or showing intelligence, especially of a high level.
Cautious : (of a person) careful to avoid potential problems or dangers.
Diligent : having or showing care and conscientiousness in one's work or duties.
Brilliant : exceptionally clever or talented.

Antonym of Reckless is Cautious