I would say Davis. He already has very good handles, and was a very solid PG until he had the growth spurt. Between the two there is definitely more potentiality with Cousins to be the best Center ever, but while Cousins has more potential. I see Davis as one of the best PF/C athletically, and talent wise. Can fast break easily, block just as well, has lankier arms, and has a capacity to learn quicker.
This is just wishful thinking. If we had either one of them, Davis especially that we'd be a contending team in 1-2 years, not to mention defensively one of the best.
Which player would you take? And please don't say Davis only plays PF. I remember him playing C, and I don't see why he won't be able to if he bulks up a little bit.
A trio of Davis, Green and Rondo would be crazy too. A team full of players with spaghetti arms lol.