French defense: Nd2 or Nc3, which is preferred

Nc3 is the best move, but requires deep theoretical knowledge to fight for an edge, particularly against the Winawer. Nd2 avoids the Winawer and would be at least equal to Nc3 (maybe superior) if not for the fact that 3...c5 equalizes on the spot (after Nc3 c5 is an unsound pawn sac)

They are both strong moves. Both are played at the highest level, and black doesn't have a super easy path to equality against either contrary to what some hot take artists on this forum often claim (although c5 is almost certainly the critical move vs Nd2 - disregarding the Rubinstein which can happen in either move order). It's chess. They're quite different tho. On the whole Nc3 is a bit sharper

While I would normally suggest reading all 39 of the articles I've written thus far in the series, if all you want are the ones where White wins, check the following.  If you do want to see all 39, simply go to the archive on the right (if you are on a mobile device, a link at the bottom will take you to the full site).

Now just keep in mind, these are not a single variation.  It will give you exposure to various ways that White can win against the French.  What you will mostly see here is 3.Nc3, 3.e5, and the King's Indian Attack.  The other articles of the 39 that currently exist are mostly Black wins with 2 draws.  All the ones where White wins are included below.

http://charlottechesscenter.blogspot.com/2018/03/the-french-connection-volume-2.html

http://charlottechesscenter.blogspot.com/2018/05/the-french-connection-volume-6.html

http://charlottechesscenter.blogspot.com/2018/06/the-french-connection-volume-7.html

http://charlottechesscenter.blogspot.com/2018/07/the-french-connection-volume-11.html

http://charlottechesscenter.blogspot.com/2019/05/the-french-connection-volume-20.html

http://charlottechesscenter.blogspot.com/2019/09/the-french-connection-volume-23.html

http://charlottechesscenter.blogspot.com/2019/09/the-french-connection-volume-25.html

http://charlottechesscenter.blogspot.com/2020/01/the-french-connection-volume-29.html

http://charlottechesscenter.blogspot.com/2020/02/the-french-connection-volume-30.html (The second of the two games)

http://charlottechesscenter.blogspot.com/2020/02/the-french-connection-volume-31.html

http://charlottechesscenter.blogspot.com/2020/03/the-french-connection-volume-35.html

I play Nd2, the tarrasch but recently I’ve stopped playing e4 and the rare occasions when I meet the French I go for two knights or kings Indian attack

@dpnorman, well said