I'd love to see a side by side comparison. McDavid is faster and that's a given. However, regarding sharp turns, edgework and for all the less "flashy" aspects of skating I did not see him enough to be able to say whoever is the best (that is to say, almost every highlights I see of McDavid are him just flying through everyone, so I can just attest that he's better than Crosby based on speed and on a more or less straight line).
People saying Crosby's skating was "fine" are out to lunch. He couldn't have been the (arguably) best hockey player in the world for most of his career by using "fine" skating. It was at the very least excellent.