the 11th and the 3rd. Some of my favorite spots are in the 11th by Rue Oberkampf-Astier,the Blue Homme, the Parmentier Metro Stop and the neighborhood surrounding it. The 3rd because I love the Marias! Parts of the 5th including Rue Mouffetard and the Hammans at the Paris Mosque as well as the Jardin des Plantes.

Definately the 6e. Tons of cafes to sit and watch the world go by, great food, street markets, fab shopping, english movies, tons and tons of great hotels....it has it all.

We stayed in the Marais this year, as it really has some of my favorite restaurants and sights (Carnavalet, Place des Vosges, Hotel de Ville) and it really is hard to beat. Although I also like the 6 and 7th. There's no reason to pick one. You should stay in different places for several trips (this was our 3rd) so you can enjoy them all. Now that we've spent a good bit of time "downtown" we may consider Montmartre next trip....but it is awfully nice to be able to walk so many places--which you can do from arrondisments 1-7.