best Paris flea market?

St. Ouen is a huge flea market and has a variety of things including furniture - a decorator's dream. I've been a few times however for me, I now choose to visit the more manageable Marche aux Puces de la Porte de Vanves. I have found more reasonable treasures here. I usually visit on a Saturday morning and it takes about 2 hours depending how much you linger :-) Metro: Porte de Vanves (line 13)

For St. Ouen, take the metro to Porte de Saint-Ouen (line 13). Edit: Janet is correct below - line 4 to Clingencourt is closer.

Happy hunting!

This discussion may be helpful:
https://community.ricksteves.com/travel-forum/france/paris-flea-market-suggestions-in-january

Vanves is also fun and small and feels more like a flea market -- but there are limited wares. Very good for framable book pages e.g. engravings of flowers and birds etc or pages from old psalters. I once got a stunning necklace there but haven't found anything to buy the last few times I went there. It is near the metro stop: Porte du Vanves. Sat mornings.

St. Ouen is the best but you have to wade through the junk on the outskirts and get into the warren of little shops in the center. I have bought nice antique Champagne flutes there and little odds and ends for the kids. There are whole areas full of antique furniture and lovely old art deco silver ware (the ice bucket of my dreams, but a few thou Euro so a bit out of the price range). It is. fun place to browse -- be extra pick pocket proof. Take line 4 to Clingencourt and then walk under the peripherique and sort of turn left into the market -- there are several connected markets, you want the ones in the center with small shops.

There are spontaneous garage sale type Vide Grenier here and there; they are often posted on signs in the area a few days before. I once got a watch from one of the first makers of watches with batteries with lovely deco design. 10 Euro and when I put the battery in it ran perfectly and has run for 15 years now. This year I got four very pretty Champagne flutes with gold rims for 15 Euro at a Vide Grenier in Batignolles. Nothing else of interest to me -- old clothes, silverware, ashtrays, dishes etc. Often, especially if they are neighborhood flea sales, there is nothing most people would want to buy -- but you can sometimes find a treasure. The watch and the Champagne flutes were literally the only things of any interest to me in the two markets I visited but both were wonderful.

"Vanves is also fun and small and feels more like a flea market -- but there are limited wares."

I've been to Vanves several times and never felt the wares were limited (-- however compared to the vast St. Ouen, I suppose that is accurate) and only once departed without buying anything. I chalked that up to it having been far too cold to be outside that day and I just kind of hurried through because I was just so cold (and yet there were a lot of vendors anyway). Most other times I left with several things.

I guess it really depends what one is looking for (I personally don't look for anything in particular other than what catches my eye in the moment). While I absolutely enjoyed my visits to St. Ouen -- it's really more fun and interesting eye-candy --to me-- than shopping. I never found much there that I was interested in buying and found it to be more expensive overall. ::shrug::

The big recurring flea markets are not places for bargain hunters. I love the glasses I got at St. Ouen, but they were not cheap. It is the sporadic Vide Grenier that are more likely to have treasures -- but also unrelenting trash. If you need art for walls -- Vanves is great for beautiful old drawings from books that are inexpensive and framable (alas the art in my price range at these places is usually awful). Old hardware like handles or door knockers can be a find. There is one place in St. Ouen that has dozens of cabinet pulls that might be a good thing for someone upgrading a kitchen on the cheap or redoing old furniture.

I agree you are better off to have only a loose agenda -- and see if there is something you want rather than looking for specific things.

On my last trip in January 2022 I had posted on TA inquiring about finding some of the random street markets. Somebody provided a link and through it I was able to find a street market that was during my visit. It ran a good ways along the Grands Boulevards. There was quite an assortment of things but I didn't find anything I had to have. Perhaps there is a market during your visit. I plugged in May 2023 and here are the listings: https://vide-greniers.org/75-Paris/mai