I always suggest 3...c5. There are 3 approaches with it.
After 1.e4 e6 2.d4 d5 3.Nd2 c5 4.exd5, you have:
A) 4...exd5 5.Ngf3 Nf6 6.Bb5+ Bd7 7.Bxd7+ Nbxd7 8.O-O Be7 9.dxc5 Nxc5 10.Nb3 Nce4
B) 4...exd5 5.Ngf3 Nc6 6.Bb5 and now 6...Qe7+ or 6...Bd6, the latter being known to give White a slight edge.
C) 4...Qxd5
So when White plays 4.Ngf3, what I suggest depends on what line you play against 4.exd5.
If you play line A above, I suggest 4...Nf6, where 5.e5 leads to the Universal System or Korchnoi Gambit. 5...exd5 would transpose to line A.
If you play line B above, I suggest 4...Nc6. More than half the times, it will transpose. Only line even slightly worth anything for White besides 5.exd5 is 5.Bb5.
If you play line C above, I suggest studying 4...cxd4, which may or may not transpose to the 4...Qxd5 lines, but the style, even when not transposed, is most in line with the positions after 4...Qxd5.
a few weeks ago i asked for help in the 3. Nc3 variation of the french. i got many answers with some people telling me to play the winawer, some people suggesting the classical and some people even suggesting 3...dxe4 to completely avoid having to deal with 3. Nc3 and the topic of this thread, 3. Nd2 separately, and to get a solid position so that i can focus most of my study in the advance variation (3. e5). i ended up choosing the winawer because i found out i was just being lazy. but now i have almost finished analysis in the winawer (only sidelines are left) and i started thinking about the next big variation i have to learn, the tarrasch (3. Nd2). the tarrasch is very solid and actually in my opinion a bit problematic for me. i will discuss why later.
firstly, i want to state is that unless i choose to become a rubenstein french player, i will not really talk about 3...dxe4 because if you are going to play 3...dxe4 against the tarrasch you might as well cut down the theory and play that against 3. Nc3 as well, and since i chose the winawer, that is mostly out of the question. so that leaves the closed system (3...Nf6) and the open system (3...c5)
3..Nf6
so the thing is from what i've seen this leads to stuff that is closer in nature to the winawer with a somewhat closed position where black plays f6 and puts pressure on the open f-file on the kingside. however, the engine thinks that white is +0.5 to +0.7 and unlike the winawer where grandmasters don't really seem to care about the computer giving white an advantage, which is shown by the fact that 3...Bb4 is the most common move after 3. Nc3 in the masters database, most masters play 3...c5 in the tarrasch and white also seems to be doing well against 3...Nf6. GM anish giri in the short & sweet version (the free sample) of his course also said that 3...Nf6 had a few tricks and was otherwise pretty meh, so he recommends 3...c5. i need the answer to why the same grandmasters who play the sharp winawer don't play these lines.
3...c5
this is considered the 'most ambitious' approach by many. against 4. Ngf3 there is this interesting move 4...Nf6, basically arguing that the Ngf3 setup in the closed system isn't really as potent, and there is also 4...cxd4. 4...cxd4 forces black to go into some of the lines after 3. Nd2 c5 4. exd5 Qxd5 5. Ngf3 cxd4 after something like 3. Nd2 c5 5. Ngf3 cxd4 5. exd5 (5. Nxd4 is also possible but i digress) where 5...exd5 for black would just let white have a blockade on black's isolated pawn, forcing 5...Qxd5.
against 4. exd5 i really am willing to give 4...exd5 a try, if it has any decent fighting chances. the modern main line is to avoid all the IQP shenanigans with 4...Qxd5, and i think it might work, but sometimes the positions feel a bit drawish although i did find one fun-looking position, but it has a 55% loss rate for black and it's not from the main line.
so overall i probably will go for either the 3...c5 with 4...Qxd5 or 3...Nf6 if i get answers to all of my questions. it would also be really helpful if you show example lines. for your information, i am looking for something where you can play for a win as black that is sound. by the way, i have also heard about some wonky 3...Nc6 lines and would like to know more about them.
thanks in advance