I personally don't think humans have free will. I believe humans actually lack the ability to 'decide' their actions. Sure, humans appear to make their decisions, but one has to realise that every 'decision' we make is based upon our experience of the world, which is based upon external factors which we have no control over.
One person's brain is composed of the same atoms as any other person. Barring any genetic mutations, which are uncontrollable anyway, humans are more or less born with the same state of mind. The difference in each individual is caused by the unique 'experience' that each individual goes through.
We make decisions based on what we know. Our knowledge originates from external stimuli. Our brains are clouded by our limited perspective of the world. We don't choose what we percieve. We just percieve what we come across. These perceptions are then combined with other perceptions & innate instincts and our brains uses those [external] factors to form what we call 'decisions'.
With all that said, I can confidently say that every choice/decision is absolutely determined by factors out of our control. If if we do have some control over our decisions, which we don't, one cannot deny the presence external stimuli as a large factor in affecting our choices in life, thus, affecting our personality.
With that said, one could say that the only thing that differs people are the things we come across, not who we are. The only thing that makes me any different from a prisoner is the different occurences we've experienced, I just had a better state of mind caused by a more fortunate experience with the world.
Thoughts?