I think that few, if anyone, could really answer this with certainty. I think that you have to take some factors into account. The first would be what evidence or analysis you have. The more you have on one particular side might be more persuasive to you in terms of writing. For example, if you can collect more information on one side over the other, I would think that this might help make the decision as to which topic on which to write, if all things were considered equal. Another element would be which one you find interesting. Perhaps, this might be the most important factor. If you are not interested in a particular topic, writing a paper on it will be painful to compose and more challenging to read and assess. Which topic do you find more fascinating? This might be one of the most basic of questions, but could be seen as vitally important in terms of the composition of your paper. For example, could you find a modern connection between assessing the factors that led to the rise of the Nazis between then and now? This might help to foster an interesting conclusion at the end of this paper. Could you find some modern connections between the causes of World War II and today? This, too, might help to develop and interesting close to the paper. I think that being able to assess which paper has more evidence and analysis and which one gauges your interest more might be critical elements to take into account before composing your work.