When I was young, my mum was a stickler for being polite. My brother and I were taught to sit up straight, address people by Auntie or Uncle and never be rude. Among the things that my parents considered rude (and trust me, there were a lot), was when we said "what?" or "huh?" when we needed someone to repeat something. We had to say "pardon?".
So that's what I say and that's what I make my kids say, archaic as it sounds. I always hear my mother's voice coming out of my mouth when I nag: "Don't say "what", say "pardon". I just can't help it. My kids? Rude? Huh?