劲敌 carries respect — it implies the opponent is genuinely strong, not just an enemy you dislike. Common in sports, business, and politics. Compare 对手 (duìshǒu, 'opponent') which is neutral; 劲敌 is specifically a *worthy* opponent.
register
Note 劲 here reads jìng (4th tone) meaning 'strong/powerful' — different from the everyday jìn meaning 'energy/strength' (有劲 yǒu jìn 'has energy').
