I've met a few but Mark Alaimo remains my favorite if only because a bunch of us met him (and Casey Biggs) in a hotel bar and spent the evening eating, getting drunk and playing darts.
He was an awesome drunk (okay, half-drunk). Voluble, funny, and extremely open about DS9. But much of what he said remains in my brain and unshared (perhaps because I know he was intoxicated).
Casey Biggs was a really interesting person. Very well-traveled, educated and curious about the fans around him. I wouldn't trade that evening for a world of gold or any amount of precious gems.
I'd like to meet the Shatman some time. Haven't had the opportunity yet, unfortunately.