How would I know what their sexual orientation is? If I did know, unless their sexual orientation gave them helpful insights into their job, I can't see it as being relevant. I suppose I would chose the one who I felt would be easiest to work with and most reliable.
I can imagine that some people may have an agenda based around sexuality. Discriminating against someone because they are straight is just the same as discriminating against them because they are gay. There are laws against this in my country.