Two of the most hax abilities in the manga. I give this to Law. We've seen more from him, in terms of haki. And I'm not sure how Kuma would push his ability.
I would give this to Kuma.
Seriously he could just blitz away from the room or push it away (if he can push the pain and fatigues why not rooms ?). And all he need is one touch to end this fight. His ability is even more hax than Law's.
I would go with Kuma. His ability is just beyond hax.
He seems too stronger and more experienced with his ability and overall than Law. Kuma is also way more durable than Law.
Also as we know Kuma only needs one touch...
Law's ability was not shown nearly that fast, first he needs to set his room then draw his sword and then slash. By that time he would be chilling in the moon. I'm also pretty sure he can just push his room away easily.
As for pushing rooms, well, he pushed several things that lack palpability such as pain, fatigues, ghost and air. Surely he can push rooms which would seem more logical than pushing pain.