We went in September last and it was very nice. Unfortunately, we go back then - have to go earlier in the year. Looks like I now also have the option of early June and pretty much the entire month of July as well. As mentioned above, it seems that there may be a lot of closures in August so I don't think that would be my first choice.

I'm assuming that by July, the city is overrun with visitors so the early June days might be my best bet.