Who would win in a fight, Arnold Schwarzenegger or Sylvester Stallone?

I'm curious to know who you guys would think would win in a fight if both actors were in their prime. Like Arnold in his bodybuilding/early actor days and Sly in his Rocky/Rambo days. I'm not talking about a fight between the characters these two actors portray. I'm talking about a street fight between these two guys themselves, no rules, everything permitted. Feel free to elaborate.