Obviously, you do you. From Google image search it seems like the world is fairly evenly split between up and down, and although I think handle up is more sane, and a little bit safer, there’s no right answer. But I grab knives off my rack in a single motion, ready to chop.

Most people’s hands can easily rotate thumb up or thumb down, so I don’t see how the direction of the handle makes much difference. If you’re used to one, it would definitely feel clunky to swap, I know I’d find grabbing a downward facing handle a bit akward.