My initial thoughts are to go with A if you feel you can improve its meandering. However, depth of thought is obviously important to convey, so C would be my next choice. B probably doesn't cut it; while you might want to demonstrate your commitment to a topic (longer paper, longer research), committees probably don't want to spend their time reading it. Plus, it's not directly related to your proposed field. My advice would be to instead talk about it in your SOP and use it to discuss your commitment and research abilities as opposed to the content itself.
Hope that helps! (Also, this is advice from someone who does not need to submit a writing sample, so take it with a grain of salt.)