Well, those are all good choices. I think it'll come down to what you want to wear.
The first one is colorful, and don't worry, I don't think you'll look like a mermaid.
It's very beautiful and says, "I'm here!"
The second is simple, but gorgeous. It's a very classic styled dress.
And the third one seems more evening-y to me, and like you said, somewhat vampy.
So what do you feel like appearing at the party, colorful, simple, or vampy? It's all up to your mood, and what you'll feel great in!