Borg Boy, hands down. I've written up the experience before. I'll dig it up and edit this reply to quote it.
Also, Jennifer Lien gave me a bad impression, though I've been told it was probably just shyness/nerves on her part. It just seemed very rude to me. The first time I saw her at a convention, as I was one or two from the head of the line at her autograph table, I heard her ask the staffer sitting beside her, "Do I have to talk to these people?"
ETA: Here's my account
of my encounter with Borg Boy.
Lein does have anxiety issues, social anxiety and what not. It's well known on the con circuit, part of why she doesn't do many appearances. She's a very shy, very quiet person, and I can totally understand that. Shame really, but ah well.
As far as Spiner goes... I didn't have any problems the two times I met him. *Shrug* But I have heard a lot from others, so I tend to think of my "fine" experiences as exceptions to the rule.
I think, from his twitter, he may just have a really weird/sarcastic sense of humor, you know? *Shrug*