Woohoo ! Looks like I'm the first to comment. Before starting on my thoughts and choices, let me say this :
Fantastic poll ! 
My take on the debate of
Choice vs Fate is a bit complicated in the sense that I have my doubts as to whether the two are different concepts at all. They seem to be just Cause and Effect going under aliases.
What is your choice today, is your Fate or Destiny tomorrow. I completely agree with Dumbledore that we are the only ones responsible for what we become, no matter what the circumstances that surround us might be. The circumstances may be factors capable of influencing us one way or the other, but it is entirely upto us whether we choose to walk a certain path or not. The precipitating factor may be anger, fear, greed, jealousy, love or anything, but the ultimate decision is ours. What if, one may ask, someone puts a pistol to your head and asks you to do something that you would never have done otherwise ? Where is the choice ? If one looks carefully, there is a choice. It may be a choice between doing that something and being killed, but there
is a choice. And there are people who have chosen the latter in such situations.
Suppose a person puts his finger in fire knowingly, what would happen ? His finger would get burned. Suppose a person put his finger in the fire unknowingly, what would happen ? His finger would get burned. The consequences in these cases are the same, though in the first one, the choice wa made consciously, whereas, in the second, the action was unconcious. Moreover, in the above instance, the effect takes place instantly, leaving us no doubt as to what caused it. What if the fire or our skin waited for a month to burn ? Would we remember what we did a month ago that has now resulted in our finger hurting ? Unlikely. But does that mean the burning was something independent, and not an effect of putting our finger in the fire, knowingly or unknowingly ? We are IMO, just unable to connect the effect with its cause for some reason and think of the effect as something that came out of the blue and call it Destiny.
I cannot agree with the theory that Fate or Destiny is something arbitrary that governs the results of our activities and also the activities themselves. What is the whole point of life if one is a mere puppet in the hands of Fate ? Surely, life means freedom and not slavery ? If we are programmed to function in a certain way by Fate, why do we resent being played with ? Is it Fate that tells us to be unsatisfied with certain situations and happy with others ? I somehow don't think so.
Chance or Luck is another factor that I am confused about. Why should chance favour someone over someone else ? Or does it just seem to, while it isn't really so ? There is an old story about a wise man telling his friend that Luck is nothing but a projection of his expectations. Keeping other factors aside, suppose one expects a good result and it doesn't happen, he terms it Bad Luck. Conversely, if the person is not expecting a desired outcome but it happens, he calls it Good Luck. Put me down as undecided as to the concept of Luck for now.
Coming to the options I would choose in the poll :
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What was the overall deciding factor of the series ?
Choice.
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Voldemorts fate: Ruled by his choice's or destined ?
Choice.
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Could Neville have done what Harry did, had Voldemort made a different choice ?
I chose other because there are so many different factors that come to play here. I don't doubt that Neville would have done what Harry did, but just that could he have done it ? Note, I'm not questioning his willingness or bravery, but his abilities. Harry had some special abilities that set him apart from most of his peers including Neville. There was Lily's protection working for Harry too. Frank and Alice would have died to protect their son, but would Voldemort have asked Alice to step aside so he could kill her son ? There are too many If's coming between answering this question categorically IMO.
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Harry becoming the owner of the Elder Wand ?
This looks like an amalgam of unconscious choice and what appears to be chance to me. Harry certainly didn't know he was going to become the owner of the Elder Wand by wrenching Draco's wand out of his grip, but he did know that he would win Draco's wand from him while doing so. Also, merely taking Draco's wand away from him wouldn't have made much difference if Draco hadn't disarmed Dumbledore previously. The balance swings towards chance and that is what I went with.
On the whole, I would have to say that I do not have any definite conclusions one way or the other, but have just thought out loud in this post and am looking forward to the insights given the people who comment on this very interesting topic.