Pure theorycrafting here, but I imagine Janna would be a good choice. Defensively, she can anticipate when the enemies will try to hit Draven (when he's trying to catch his spinning axes) and put up a shield to protect him then. Furthermore, her shield also increases attack damage, so it combines well with Spinning Axe's percentage damage increase based on total attack damage, so Draven can deal tons of damage. Janna can also use Howling Gale to create opportunities for exchanges (and Blood Rush could help Draven chase to deal more autoattacks when he chooses to poke, which also syngergizes well with Janna's slow from Zephyr). Even Janna's passive helps in those situations, plus helps him catch spinning axes. Overall, with Janna supporting, Draven will have a very easy time coming out ahead in exchanges because he'll be able to do so much damage with his combined Spinning Axes, Wicked Blades, and Janna shield.