I third the Tarrasch. Active, classical chess.
I fourth it. The only time I don't play the Tarrasch is when I try to throw them off balance. Then I play the Old Benoni; 1. d4 c5. Speaking of mental edge ;)
hedgehog fifth row dominance
d4 e6 c4 Ab4+ Ad2 a5 Axb4 axb4 Cf3 f5 is a good system, but modern benoni is good tactical defense!
Benoni is good if you are not afraid to sacrifice the pawn.
There are some players that were not comfortable with sacrificing the pawns like I am. I know that sacrificing pawns to gain compensation is good but yet I'm not happy with down a pawn.
The only theory I didn't know on 1...Nf6 is the trompowsky one which goes for 2.Bg5 immediately.
When in doubt of the Tromp, just play 2...e6 and develop normally.
You can still play the French against d4
i suggest the modern benoni
I second the Tarrasch suggestion : 1.d4 d5 2.c4 e6 3.Nc3 c5