Paris parks

Years ago I was in Paris with a friend in October. We rented bikes at a street corner on the edge of the Bois de Boulogne and spent a lovely day exploring and enjoying the park in its fall colors.

Bois de bologne if you want to rent a rowboat and paddle about. Here are some snapshots of a day we spent there.
http://janettravels.wordpress.com/2010/05/29/monday-in-the-bois-with-ed/

Otherwise IMHO the most interesting park in Paris is Butte Chaumont. It is quite large and makes for a fun wander to locate the grotos and waterfalls as well as climb up the artificial mountain.

Another possibility is the Promenade Plantee
http://janettravels.wordpress.com/2010/06/14/promenade-plantee-turning-discarded-public-space-into-a-pleasant-place-for-parisians/
This is an old elevated rail line that runs from the Bastille Opera to the Vincennes. It has been turned into a long garden and you can stroll, picnic and towards the end it goes to ground. It is a pleasant way to wander through (and above) parts of Paris you might otherwise not see. The entrance is just past the Opera House above the shops that house art galleries and such under what looks like an old aqueduct but is an old rail line.

Luxembourg Gardens is my favorite but my second favorite would be the Parc de Bagatelle in the Bois de Boulogne.

Thanks for the replies! I appreciate the new parks to check out too! Decisions, decisions....

The Bagatelle is absolutely lovely especially if you're a real flower lover. I don't know however how spectacular it would be in early October; it really shines in the spring and early summer, but I've never been there to see their fall plantings.

Of the three you listed, I'd choose Monceau. Much smaller than the others, in an interesting neighborhood. But you really can't go wrong with any of them.