Which argument, the functionalist or intentionalist argument, do you think has a higher chance of being correct based on the current evidence available?
i.e. which argument do you agree with: the Holocaust was always the plan of the Nazi regime, or, the Holocaust was more of a spontaneous plan that sort of evolved over time, or was an example of the Nazi's just clutching at straws.
While you await newer answers, /u/commiespaceinvader addressed the intentionalist / functionalist debate in this thread, which also links to some other relevant threads. There is also a relevant episode of the AH podcast.
I would say that today most scholars are actually moving away from looking specifically at one or the other, and looking at it more holistically, using both arguments. This is primarily because it was so broad, and conducted so differently in different areas, a functionalist, and an intentionalist argument can be made fairly persuasively. Personally from my research, and my understanding of contemporary scholarship, these models don't tell us as much as we have hoped, because they are almost too simplistic, and are also both true in different ways. There is significant evidence for a murderous form of antisemitism being present in the Nazi party from the get go, but did they have a plan for Auschwitz by the time they had built Dachau? Probably not. In for example Hungary, the model was absolutely intentionalist, they went in with the infrastructure for mass killing already functional, and a plan for mass killing already laid out. But can the same be said of Poland? It's unclear. For the most part, Holocaust scholarship is becoming more local, particularly with the publication of Neighbors, Death of the Shtetl, and the increased research on places like Romania. These will often use either a combination of the functionalist and intentionalist arguments, or will possibly lean more towards one side, but more as a way of examining local circumstances, than as a way of defining one overarching theory for the Holocaust.