My female was 1 year old when she way spayed and she is a, for lack of a better word... bitch.
She is not really aggressive but she does growl at my younger boy as a warning if she has a toy or a bone. I'm just lucky my boy is so forgiving, he doesn't have a mean bone in his body!
When we go to the park around other dogs she is as sweet as pie, even with toys, it's just at home
I don't care what anyone says, spaying is the responsible thing to do, even if it doesn't alter their behavior it has a lot of health benefits.