Hmm, very interesting choice. I wonder what's Kurono's reason for bringing Nishi back. You'd think that by now, Kurono has at least a much information about the whole Gantz thing as him. But then there's that website that Nishi ran, where he was talking about the world being doomed and all. Probably the only reason for bringing him back.
Another reason could be the fact that it's hard for Kurono to bring back either Kishimoto (still a bit heartbroken/jealous?) or Sei (past girlfriend, didn't want to face her yet now that he has Tae?).
But Kei still has his points to spend, so I wonder who will be the last one to be chosen. Perhaps it's better to choose for the badass weapon at this point, to ensure survival of everyone he brought back at this point.