Europe: I have been advocating for Europe because I have never been (okay, I have but I was a baby and I don't remember so it doesn't count) and I have always imagined my honeymoon being the opportunity to travel in Europe for a while.
Thailand: My honey is advocating for this one because it is beautiful, cheap, and exotic. Plus, it makes sense to use a long vacation to go to a location that is more difficult to get to. We could always go to Europe for a week-long vacation, but that would be much harder with Thailand. And it is awfully picturesque: