What are the peak hours for public transportation in Paris?

In general, the peak hour in the morning is about 8:30 to 9:30, though this can vary a bit depending on which line segment and which direction.

I’d say the peak hour in the evening is around 17:30 to 19:30. Here there are probably even more local variations.

Note however that July and August have less traffic than other periods, and they cover the school holidays, and many people take holidays during that period. The lowest traffic is probably observed first half of August, followed by second halves of August and July.

But as those are school holidays, there are actually less trains/trams/buses than during other periods, so you could actually end up having more people per train/tram/bus.

The question, which has evolved somewhat given the comment, and could be now considered to be one of those requests-for-opinions questions, which the moderators don't like. I would have liked to add this as a comment but I don't have the points yet. If you like the answer you can put me over that threshold, hint hint hint.

If your desire is to maximize the experience of Paris on the street, her architecture, parks, street life, and the chance to examine at close hand and your leisure some spot of interest then I commend to you, as part of your studies of the French language, the word Flâneur.

The core of Paris is sufficiently dense as to make a set of walking tours, either just you swanning about, following routes from books which have routes marked out, or formal walking tours offered or some combination, worthwhile and alleviate the requirement of using public transport.

I know that the buses in off-peak hours will be sufficiently swift as to preclude any reasonable chance of much enjoyment of viewing what you can see.

Most museums in Paris would be madhouses in July, with the possible exceptions of the Musée de l'air et de l'espace and the Musée de la musique and I've found attendance on autumn Saturdays in the former to approach the level of annoyance.

Peak hours aren't really a thing in Paris (although expect more passengers between 7-9, 12-13, 17.30-18.30), moreso in July (quite a lot of tourists).

General travel in Paris advice :

My advice, for any long trip take the metro (don't go to the ticket machines if possible, got to the desks RATP agents tend to be really helpful as long as you're polite), depending the number of trips a day ticket or a 10 trips may be the best (if you're travelling in the same zone).Once again, the best is to ask the RATP agent on site and they'll get you the best deal. For the trip hotel/airport depending on where is your hotel the RER may be the best solution, taking the taxi is really expensive but may be more convenient.

In the metro/RER, like in any other big cities, be mindful of your possessions and read the mood. If everyone is shutting up, keeping to themselves and are blanked eyed, now is the time to not stand out and do the same. If everyone is lively and are chatting, there may be an event/concert etc.., ask around (politely) could be an opportunity to do something unexpected.

For short distances, get a good pair of comfortable shoes (and it will be a blessing whilst queuing).

If you need directions or tips (where is the closest cheap and cheerful eatery, etc...), start any interaction with "bonjour" during the day or "bonsoir" at night, even if you don't speak French. It's a standard and even if you are the nicest most polite person if the world, if you don't start a conversation by saying hello under French standard it will be considered extremely rude.

A simple "bonjour" and an awkward smile will often open you a lot of doors and get you around in a more efficient and cheaper way.

If you don't speak French, younger people (18-35) will tend to have a better grasp of English than older people. Otherwise it's like in any city, if you see him/her fast pacing, don't bother he/she is going to work/class etc...

If you are a person of colour, openly gay etc... be mindful that 23% of French people voted for the Rassemblement National in the European elections (extreme right generally racist/xenophobic conservative party). So some of my compatriots may not be as helpful as they can :/ , although most people are fine with you.

I'm painting a bad picture but in reality as long as you follow the Wheaton law, everything is going to be fine.

Have a fun trip and take the time to "boire l'apéro en térasse" !