Bought Ahri and played my first match with her. Very fun. Stacked spellvamp late game, makes her very survivable, since it's quite hard for a single target to focus you down while your ult is up, and by the time you've moved away and someone else has turned on you, your spells have already hit 30 things for over 9000 damage.
I think W is actually her best skill to max; it's the only one that gets a reduced CD, giving you something to spam while dashing around, it has the best damage vs a single target or multiple spread out targets, and it's very mana efficient, and it's cost doesn't rise with level like the others. Obvious problem being, it's shorter range than the orb. But if you landed E anyways, that won't be a problem, and if you didn't, orb is mostly good for blowing up creeps or enemies retarded enough to line up for you. (Though admittedly, her ult lets her line up enemies herself.) I was initially wondering whether AP is really the best investment or if CD or spellpen would be better, but after playing her I have to say AP + Spellvamp really is the best. Most fights are going to happen around creeps, and the AP lets you leech that much more life while popping them, and you can easily target whoever has the lowest MR. The CD on the ult feels really short.
Also, best part about the ult: you know when you're in/near a fight and some fucker is escaping with 10 hp a whole screen away? This is the ONLY fucking hero that can just run over and fucking pop them. Dash through their whole team while doing it too, you'll just crank more damage out that way. Feels SO much better than hanging around the edges with a normal mage trying to reach their squishies without getting crushed by the tank, or just blasting the tank because he's the only thing you can reach.