I saw Garret, John de Lancie, and Armin Shimerman at my last con in '95 (though some might say that's an antiquated memory), and Armin was great, even in a large hall. Someone asked where he was from, and in his inimitable voice, answered "Joisey! Can't ya tell?"
John dL. seemed a bit uncomfortable with Q-specific questions, but was more receptive to questions on his career. The worst moment came when:
: Have you accepted the Lord Jesus Christ as your Personal Savior?
: (pause) Next question?
Sadly, I don't remember much from Garret as the show hadn't been on long (local tv promos mispronounced his name), so I might have been checking the dealers room.