拒绝 (jù jué) is the standard, neutral verb for 'refuse, reject, decline' — it works in most situations, from turning down an invitation to rejecting a proposal. Compared to 推 (tuī 'decline politely') and 退 (tuì 'withdraw/return'), 拒绝 is more direct and can be used for both people and abstract things. 否定 (fǒu dìng) focuses on denying a statement, while 谢绝 (xiè jué) is a more formal, polite way to refuse.