Louvre

Some doors/entrances are better than others. I think I read this in the RS guide, so maybe start there?

I like to use a google feature to find out this type of info. If you google:
Louvre Museum France
the page that comes up (NOT the Louvre website), you will see an arrow down the page a bit that says:
More about the Louvre
click on that and you should see a chart that shows popular times, and you can choose the day of the week.

Most places have this chart, I often have a look when deciding when to visit a place.

We went to the Louvre last Friday when it stays open late, until 9:45 pm. We got there pretty late, a little before 9 pm. There was no line to get in at the pyramid entrance. Of course, getting there that late meant that we didn't really have much time to really explore the museum, so I think we were kind of those annoying tourists that just went to see the Mona Lisa. I was unsure if we would end up going to the Louvre because I had heard about the crowds, but my 10-year old wanted to see the Mona Lisa in person, so we went by on our walk back from the Arc de Triomphe and found no line and went in. We also had a museum pass.

A museum pass is not going to help you skip many lines at the Louvre; the line for people with passes for security is often longer than the lines at other entrances.

Friday evening would be my choice, go after 6:00 pm and you'll have almost 4 hrs to explore and it's usually not that crowded then, except for around the Mona Lisa where it's always crowded.

But first ask your self why you want to go? If you love the art that is in the collection then do it and have a great time! But if its just because you have heard its a so called Must See, then i lay money that there would be other museums in Paris that were more to your taste that you would enjoy more😀
Mona Lisa is not a Must See in my books, now Monets Water lilies in the Orangerie.......