Is this your first trip? Do you plan on returning? 10-days spread over 3 locations doesn't allow very much time in any. If you don't want to spend all your time in Paris, I'd recommend only one other location, and then one which has a nice contrast to Paris. Nice won't give you that. I'm partial to the Loire Valley, which is on a couple of hours from Paris by TGV, or Provence. However, Paris is a city to be experienced slowly unless all you want to do is "collect" landmarks.