Ok, first off I am 11 so I am definitely not an expert on horses. But, out of all the horses I have ridden at the barn where I ride the females are much calmer and gentler. So from my experience I would choose a female. Also, older horses tend to be calmer than younger horses.
I know what it feels like to have a fear of horses; I've been close to being dragged before. When you ride a horse, ride through your fear. I had a fear of cantering after a bad experience, but now I am more confident as I have been cantering more. Actually, it was a male horse I got dragged by, and in order to build up my confidence again, I rode a female horse that was older. Just keep trying. That's what I do. And, take small steps in order to build up your riding level. Practice the posting trot for a few days. Then, ease into practicing the sitting trot, and so on.
i <3 horses!!!!