Weird, this is the 1 attack that never managed to hit me, it's always just a free hit for me (unless he lands so far away that I have to sprint for half an hour to reach him...)
I pretty much always circle around bosses while walking backwards, and usually to the right. When Artorias does that massive leap thing, I just dodge in the same direction as I'm moving, while he's at the highest point of the jump. He'll miss by miles.
Or did you mean the other, smaller jump, where he somersaults and then hits you with his blade? That 1 is significantly more annoying to me, but I can usually dodge it if I start he dodge the moment he's done somersaulting. If I'm lucky, he'll do it again, but the second one will then have crappy tracking, so he totally attacks the wrong direction as long as I keep circling. Free hit for me.