Kenpachi got this.
I kinda agree with most of the people here but where did Kenpachi get his rise in power? when you think about the last fight he had with Ichigo, Kenpachi's eye patch came off the yet Ichigo still was able to keep up with him right? and this happened before Ichigo could release his zanpakutō also it doesn't make any sense with Ichigo's recent rise in power, Kenpachi shouldn't of been able to beat Nnoitra. The fight's between Grimmjow and Ichigo was far more intense then anything Nnoitra or Kenpachi had done in previous fights. Feat wise Grimmjow seemed far more superior then Nnoitra in terms of raw power and speed and he had a brief fight with Ulquiorra was pretty impressive. So logically Grimmjaw should be able to win against Kenpachi.
Imho I say Grimmjow would win 6-7/10 taking the majority