I have only been to two conventions that had star trek actors.
The first was the Peterborough convention where they had over half the VOY cast and four from DS9. Rene and Nana were both really nice when i got their autographs. And Rene was really funny onstage as well.
Robert Picardo and Ethan Philips were both hilarious they even did a comedy act together. Both Garrett Wang and Robert Beltran were a lot more funny and likable than i expected given how bland/dead the characters of Kim and Chakotay could be. Jeri Ryan was fantastic.
The second was the Wrexham comicon that took place last sunday and had John Billingsley in attendance along with his wife Bonita Friedericy who were both lovely. I spent a half hour or more chatting away to them and they were giving away free Italian candy