Best Flea Market in Paris?

Best thread EVER. I'm totally following!

Puces de St-Ouen is the largest.

Whether it’s the best depends on what you are exactly looking for.

I like Vanves. It is small and manageable and I have managed to find little treasures every time I have been there. The large one at Clingencourt has regular antique stores and such in the back and tons of booths out front; when I was there years ago, it was mostly total junk. I remember acres of used phone cards and such and lots of fake leather coats and general trash.

There are also Vide Grenier (basically yard sales) here and there announced on fliers and I managed to get both a wonderful old necklace and an art deco design wristwatch that has kept perfect time for 10 years now and gets lots of comments. Each was 10 Euro. At Vanves I got a nice necklace one year and a cute frog pin for my granddaughter another as well as old prints.

Vanves is my favorite. As janet said, it is small and very manageable. You can actually get fair prices there. The St Ouen flea market at Clignancourt is the largest in the world and is overwhelming. Many, many buildings with lots of sellers. We saw mostly very nice things there (furniture, silver, rugs, jewelry, etc) all expensive. Did not find one bargain.

I will add my vote to those for Vanves. We have had very good luck there in finding unusual things for fair prices. I haunt garage sales in the States, and I find better prices for the antique woodworking tools I collect in France. My wife got real bargains on a collectable art glass plate and a delightful and very old artist's sketchbook the last time we were there. Get there early on a Saturday as they are setting up to score the real gems.

Another vote for Vanves! IMO it is just the right size.

Not a “flea” market but Rue Mouffetard is great shopping.

Depending where you are staying, you might try weekend mornings at the Place d'Aligre market. Can't vouch for "les puces" but the old stuff scattered around might rate as junque.
Otherwise, here's a list from a Paris guide website: https://www.parisperfect.com/plan-your-trip/things-to-see/markets/paris-flea-markets.php

I love the small neighbourhood vide greniers. Website and the have an app. Some are like a neighbourhood yard sale, others have a mix of booths of antique dealers (expensive) and inexpensive tables with stuff ie kitchen ware. Hint: look in boxes under the tables if they are out in the open for the best deals. I saw others rooting through boxes so I joined in. Perhaps ask first if it ok to do so.

https://vide-greniers.org/75-Paris

I have found some great scarves at neighbourhood vide greniers for very little money. I took them back to my room and washed them in the sink with the powdered laundry soap I had and wore them during the trip.

I have only been to Clingencourt once; it is huge. I had a couple of maps that I saved as photos on my phone and that helps. I went with a friend. Not sure I would have tackled it on my own. Based on the feedback here I might do Vavnes by myself.

Another vote for Vanves--easy metro ride, little bakery on the corner, just big enough to keep me busy for a good 2 hours and the sellers were open to bargaining, though I don't do that unless it's a costly item. If you know collectible prices from such shows at home I'd say they were pretty much in line at Vanves. I came home with an early 1900s carved wooden pocket watch case--a souvenir of Fontainebleu--2 sets of vintage glass buttons and some embroidered trim for my knitted sweater projects, some chalkware santons figures and a sterling ring of a repousse fox & grapes. I go for small items, but there was a good variety of unusual collectibles, jewelry, some clothing & accessories, paintings & other bits of art, ephemera and just the usual vintage household stuff but French and therefore much more intriguing :) It was all vintage, no new garbage or garage sale stuff. Even if I couldn't bring everything home I sure enjoyed just seeing it.