The thread Susan linked above is a pretty thorough recent "where to stay" discussion. I've stayed in three parts of Paris -- Latin Quarter (5th), Marais (4th) and Montparnasse (14th), and was happy with them all. There are many good choices. A couple of general ideas come to mind: (1) the closer to the river, the more convenient for sightseeing and the more it will cost; and (2) having a Metro station within a few blocks is always helpful, especially a station where two lines intersect.
You'll get lots of opinions in response to your very broad questions. It would help to know what your price range is. I suggest using booking.com to look for candidates, it has useful filters and the reviews are authentic. For a July trip, air conditioning would be a worthwhile consideration. And Google street view helps you eyeball neighborhoods around specific places.
Rue Cler isn't a bad place, but I'm not a fan for two reasons: (1) it's farther from most sights than many alternatives, and (2) it's overrun with Americans clutching blue and gold guidebooks (maybe not so much under Covid conditions). Our host dropped the Latin Quarter hotels from his guidebooks, I guess to save pages or research costs, but certainly not because of lack of good hotel choices there. Good luck with your planning and your trip.
EDIT -- Just read Pam's post above, her comments are always on target. She's right about booking directly with your hotel, and springing for a rate where you can cancel not far ahead. What she observed about Rue Cler in the fall may not hold as true in peak summer season. At least you're not going in August, when Paris empties out and foreign tourists are thick on the ground. ;-)