I like smallish groups best, about 4 or 5 people. It means there's enough ither people to keep the conversation going and you can just chip in when you feel like it.
When the group gets bigger than that, it's harder to get a word in edge-ways and so I start to feel anxious that I'm feeling left out. Or worse, when the big group starts to split into 2 smaller groups and you find yourself part of neither, just sat alone looking like a prize turkey.
But when I'm with just one other person, I get nervous as there's much more onus on me to keep the conversation going. I usually end up worrying so much about what to say next that my mind just goes blank. I hate awkward silences. To be honest, I can't really imagine ever getting over this aspect of SA. If you're no good at making conversation, then I don't see how you're ever going to form meaningful relationships with other people.