I've got a son and a daughter. I'd rather my son was gay than my daughter in porn.
There's no shame in being gay, where as personally I couldn't say I feel the same way for having a daughter as a porn star... It's certainly not something I'd want my daughter involved in.
I would think this right here would be a big factor in how people answer. I think people with a daughter, even if they also have a son, would be less likely to choose porn.
Also I'm sure if the question was asked to women the answer would be overwhelming gay son. But with men, at least from I have noticed by asking people in person, I have been surprised by the number of people that either can't choose or choose daughter in porn.