Much of a muchness, I think, eat? 
They're both informal. That isn't going to make anyone stop answering a question, of course. But if you know one is a bit rude, why use it?
I wouldn't dream of responding to an email from a person I didn't know, in a rude or less considered way, just because of how they wrote it. If they didn't know how to write a formal letter, or if they couldn't spell, or their English wasn't very good, I would still reply to them as politely and carefully as anyone else.
But, if you're in the position of writing the email, definitely I'd recommend writing it with formal phrasing, because it is considered more polite. And, sadly, sooner or later someone will judge you for the informality, so it's best to know.
FWIW you can usually tell who's being rude/lazy and who simply doesn't know: the whole tone of the letter can be very polite despite having a 'Hello there' at the start. But often, someone who starts off by being informal will also not show much awareness that they're in a formal context, and that can be annoying.