多么 (duō me) is an adverb used in exclamations ('how ...!' or 'what a ...!') and in concessive clauses meaning 'no matter how'. It is neutral in register and common in both speech and writing. 哪怕 (nǎ pà) is a conjunction meaning 'even if' and introduces a hypothetical condition, not an exclamation; 何等 (hé děng) is a literary/formal synonym for the exclamatory sense, rarely used in everyday conversation.