We went at the beginning of July last year and the weather was a bit cold and rainy (60's and low 70's) but it was a blast.
I highly highly highly recommend the Lenox Montparnasse hotel. It was a tad "out of the way" (3 metro stops from tourist areas) but a charming hotel where the staff was wonderful, the rooms were small but comfortable, and the price was fantastic for what we got (location/room). I would stay there again in a heartbeat.
There are two pastry shops right there and a supermarket and it's not in a touristy area so things are less expensive. Two different metro stations are within a block in either direction. Couldn't have been easier.
I loved Paris and can't wait to go back.