Whoever is brave enough or impatient enough or aggressive enough to go first is how it seems to play out. This is a good thing in my opinion, because I really don't like sitting in a stalemate where my way of doing things (I'm usually in camp A) conflicts with their way and no one is brave enough to just go. So now you have a full intersection of cars with cars behind them and someone (maybe me) is going to get impatient and just go (usually at the exact second the other person decides the same thing).

So I tend to be more aggressive and just start out slowly ready if the other person does the same thing if I perceive it to be "my turn".