First time in Paris, June or September?

I can't speak to June. I've been to Paris in September at least three times. The weather was glorious. I felt it was busy, but my understanding was that it was less busy than summer. I thought Versailles was quite crazy, but everything else felt comfortable and manageable. Depending on what you are used to, for me personally, air conditioning would still be a must.

I remember reading on this forum that September is actually a very busy time for Paris hotel rooms due to a large number of conventions that are held during this month.

Paris will be busy, no matter what. However, if I remember what I have read correctly, June should be a better time for hotels. I think the weather can be fine either time. I was there in June this year and it was great.

Up to the middle of June is fine, last 2 wks of June not. I’ve spent many June’s in Paris, including this year, and the difference is night and day.

This year it was Saturday, June 16, when all of a sudden Paris went from not a lot of tourists to an overwhelming amount, with massive lines almost everywhere.

Hotel prices are about the same either month but many will go up a bit before, and during, Paris Fashion week which is Sept 25 to Oct 3rd this year.

One objective difference is that in June, the days will be longer. Otherwise, weather is what it is, and with climate change, it's less predictable all the time. I'd definitely want air conditioning in June (I almost needed it in May 2018), and maybe in September as well (although it shouldn't be necessary then, as I said that's no longer predictable).

September is indeed a busy time due to conventions, fashion shows, etc, but you have enough lead time to get a hotel for either June or September with no problems. As for crowds, the big sights are always crowded, and I'm not sure it makes a difference.

Everything except prices of hotels are better in September. September is the best month for Paris IMHO; it is also the month with the most demand for hotels and hence highest hotel prices. June is already into high season though and schools are out most places so also very crowded. I would always choose September if I could travel then and now that I am retired, we do choose September and October. We like it a bit cooler and so October works for us. We will be there all this October ourselves and are traveling elsewhere in Europe in September.

All else equal, I would opt for June for the two reasons already indicated, hotels and hours of daylight. But both are really top-notch times for a visit, so don't fret about it if Sept. is better for other reasons.

Great sights are justly popular and can be crowded year round. Also year round is a neighborhood or park a walk or metro ride away that will be free of tourists. Plan your days accordingly, and you will have a great time!

First two week of June, almost any week in May (I know not one of your options) and last two weeks of September are great times to be in Paris. I find it is very busy in Paris in September but not as crowded at the tourist sites as it is in July and late June. I had a similar experience to Susan in 2011 when we spent 6 weeks in Paris from May 31st to July 14th. Suddenly around mid-June, it became very, very busy.