[wdwsurprise]

We have done it before for my wife's 40th. We stayed in the Hotel Korner Eiffel - Small, friendly hotel, just 5 mins walk from the Champ Du Mars and the Eiffel Tower. Great location for exploring as only 2 minutes from the Metro too.
If you want to explore Paris, then definitely stay there - 40 mins each way eats into your sightseeing time if you stay at the parks - especially as you will be on and off the metro all day to explore everything as well. Would recommend a boat tour down the Seine - very reasonably priced and you get a good overview of the main sights.