I guess I'll have to disagree with you guys. There may be more to being human than emotional displays, but emotional displays are a huge part of being human. For Kirk to say that Spock was the most human, despite rarely showing emotion, seems ridiculous.
It'd be like Picard insisting that Data was the most human individual he knew, or Sisko saying that Odo was the most human. It'd make for a nice speech, but it seems to lack in truth.