Lifehacker on signing-off emails: The Yanks might think “Cheers” is too “mock-Brit”, but Australians are comfortable with it.
Personally I use Cheers on most. Regards on formal stuff. Or nothing when I’m talking to a regular correspondent and am in a hurry and/or on a mobile.
An older Lifehacker article noted “Best” was awkward. I hate “Best”. What does it even mean? Best what? Maybe in American English it has some inherent meaning, but to me just reads like it means “Best regards” but that the sender is too damn lazy to type “regards”… in which case it’s not really best, is it.
And starting off emails? I often say “Hi X,”. Some others say just “X,” then go on with the message, which I think sounds a little curt, but I guess it isn’t, as plenty of people, even those I know well and get along with famously, use it.