If you were flying into Paris on a budget European airline, and price-wise and time-wise it really didn't matter much if you were to fly into Orly or CDG, which would you pick? I realize this might differ based on the location of my accomodations in Paris - I'm not yet sure of my hotel but it will be metro accessible within the city.
In your case, I'd prefer Orly. Baggage handling is faster, the two terminals are a lot smaller than CDG, the Orlyval runs right past the terminals, and the RER seems to be less crowded coming in from the south end of Paris. And, unless you happen to be staying in north Paris, you won't have to go thru Gare du Nord station. As well, the Denfert-Rochereau station is a good place to transfer to the Metro for most places south of Gare du Nord, rather than going thru Chatelet, another very busy RER-Metro station.