I'm going to Africa in October and i have a 48 hour stop in Europe before flying to Jo-berg. I have the option of first flying to Amsterdam, Paris or London. I have never been to any of them, but my wife has been to Paris.
Is there a particular site in any of those cities that you really want to see? For example, if you're an art lover, Paris would be my first choice. In general, they all have worthwhile things to do in such a short time so you couldn't go wrong in any of them. As noted, Amsterdam is smaller so logistically it would be easier to manage for a short visit.
Voice of dissent: I would skip Amsterdam. There are cool things there for sure, but not to the scale of London and Paris. Also, it's dirty and you will get robbed.