We can't really tell simply from the pictures since the techniques are not used on the same enemy.
I imagine that Zorro's techniques is more powerful since it can cut through iron, we still have to see if Yahazu Giri can do the same.
Yahuzu Giri and Zoro's techniques are seriously different. They both use different styles anyway, and they're both just one move that they both have. Although, overall, I'd say Zoro's is better because it works on steel and is faster, while Brook's has the dramatic delay.