2.e4! FTW
1.d4 d5 (2.c4) (2.Nf3) (2.Bf4) or (2.e3)― pick the best move.

c4 is the move that demands black answers a specific problem immediately i.e. exchange or support the d-pawn. That would be my preferred move because it is the most active.
c4 is the move that demands black answers a specific problem immediately i.e. exchange or support the d-pawn. That would be my preferred move because it is the most active.
1.d4 d5 (2.c4) (2.Nf3) (2.Bf4) or (2.e3)― pick the best move. Explain your reasoning.


Encyclopedia article: http://en.wikipedia.org/wiki/Closed_Game
Computer analysis (~3300):