Three-Way Numbers

I love group sex, it doesn't matter if I'm participating or watching, I love it.
I was thinking about couples that have three-ways, and was pondering what the numbers are. What I mean is, are there more three-ways with one woman and two men, or with two women and one man? How does it work out in real, every day life? Are women more inclined to participate together, side by side, or are men? (I'm talking about straight people here, not bisexuals, although that's another, interesting question.)
I don't have an answer, and I doubt it's something that could be easily researched.
What do you think?