I'm still pretty formal with new clients. It takes me years to leave out a valediction with some. But on the other hand, my favorite valediction is usually "Cheers," since it seems the most casual and least demanding. Still, I always worry this gives away the fact that I'm an alcoholic.
My runner up is "Yours," which I see didn't make the list.
My runner up is "Yours," which I see didn't make the list.