We were there last July. Great trip so I'd say if you can only go in July, go. We rented an apartment in Paris (
www.vacationinparis.com) and it was the way to go. One good thing about a hotel is that it likely would have had a/c. There was a heat wave last summer and few apartments have a/c (rental or otherwise), so it was hot. The crowds at tourist spots were big. I've spent quite a lot of time in France before so we did not feel the need to go to the Louvre, try to get into Notre Dame, etc. We walked around them but didn't go in, there were huge lines.
We spent a week in Paris and then did another week traveling around the country. It was a nice balance. Personally I'm fine with just walking around in different neighborhoods, eating here and there. We went to some smaller, more quiet museums. If you haven't been to Paris before and are counting on going to the major sites, then it might be a different story and I'd go during off-season. I love October in Paris.