Best fois gras in Paris

It's the wrong time of year for that. The two months leading up to Christmas are the best, so unless you find someone with a supply of fresh livers you'll only get canned, cooked, or semi cooked

We did a walking food tour in Paris on 29 Feb. One of our stops was Maison Godard, Foie Gras PARIS. The foie gras and pates were all canned but the owner was very nice. We did tastings and really enjoyed both the foie gras and the rillette of duck, often sold in a glass jar.

I assume you mean foie gras to eat at a restaurant.
In this case the restaurants offering South West cuisine are probably where you will find some good foie gras.

That being said, the “best” foie gras does not exist. It all depends on how it is prepared (with what kind of seasoning) and what we are talking about when we say "foie gras" (with an E and not fois gras with an S).
The only authentic foie gras is a whole foie gras "Foie Gras entier"
Other names are foie gras reconstituted from the livers of different animals or preparations not containing only foie gras.

There are also 2 kinds of foie gras, duck and goose which have a different taste.

It's not necessarily a bad time to eat whole foie gras. The force-feeding of animals can be done until spring. Where I live several neighboring farms force-feed the ducks until April even though the demand is much lower than in December.

And if you are looking for canned (cooked) foie gras you will find it all year round.

Le Comptoir de la Gastronomie.