I think one of the interesting things about Star Wars is that it's NOT simply nature vs. nurture, destiny vs. choice. I think both sides of the argument are built into the movies rather symbiotically and run in parallel. Anakin, for example, is The Chosen One. That is the destiny part--he is DESTINED to destroy the Sith and bring balance to the Force. That in itself is pretty deterministic. However, I think the other message is that, while destiny shapes the galaxy of possibilities we face each day, that it is also sometimes difficult to make one's destiny happen. That is where choice comes in--and it was not until Anakin realized he had a choice of whether or not to fulfil that destin that he finally suceeded. That is where free will comes in. Luke faced two possible destinies: to follow in his father's footsteps and become Darth Vader, Jr., or to choose his own path, which he ultimately does.