"Theoricallyly, Nc3 is better than d3"
Thats wrong and this assesment is based on old theory.
Nowadays, almost nobody at top level plays Nc3 because of the line 3.Nc3 fxe4 4.Nxe4 Nf6 which leads to drawish positions, although white is pawn up.
This is discussed by Silman here :
http://www.chess.com/article/view/the-jaenischschliemann-gambit
Here we will discuss what happens if white plays one of the mainlines, 4. d3 in responce to the Schliemann, and how to deal with it.
Theoreticly, Nc3 is better than d3 but both are the main lines. I will cover Nc3 in another forum.