I have to agree with lizzie. I have had such bad experiences with mares in the past, that I'v been put off!
For example, I had a mare who was really really sour, and mareish. I went into her stable one day, and for no reason that I could see, she whipped her backside round towards me, and gave me a solid kick in the leg. I was very lucky that she didn't have hind shoes on, but all the same it hurt.
There wasn't just the one either. Several of them, I have had close encounters with, and that really put me off.
I just don't want that again, nor do I want to waste petrol and time trekking up and down the country looking at sour mares.
I'm not saying, if I get a gelding that it will be guaranteed to have a perfect temperment, but with me, they have a better track record!