I don't think there's a single one of them that couldn't be worked on, or a connection made, in the 5 minutes you get with them. They're not totally like the characters they play, but that would be stupid to expect.
Walter Koenig was the friendliest. John De Lancie looked at me with interest, but I was too shy to connect. De Kelley was the most solid. Leonard Nimoy the most aura-ed. William Shatner was a bit 'so f**', at that time, but wasn't rude at all. Well humoured.
I've met six of them since 2004, and I'm going to get my photo ops retouched, cos I look terrible in them. And, I'm going to meet as many of them again and get another lot!