I think calling either Luffy or Kidd useless is bullshit.
If we really have to pick one of the two with the contest of the 1st mates then:
- Zoro had to carry Luffy when he was temporarily KOed on the Live Floor by Apoo, he also had to carry him on the rooftop when Luffy ran out of stamina post-G4. When Luffy was temporarily KOed another time (by Kaido's Ragnarok), Zoro had to save him with his last attempt against Kaido (Ashura).
- Killer's cover was blown up by Kidd and later, fighting Hawkins, he found himself trapped in a twisted game with Kidd's life on the line.
I'd say that, during the raid, Zoro was troubled more often and sistematically by Luffy, resulting in more serious injuries too.
Killer wasn't troubled at the same rate by Kidd, but that time he was really risking his life in a lose-lose game that he had to overcome with his brain.
Overall, Zoro had more trouble cause of Luffy.