MNb wrote on 09/25/07 at 21:53:31:
NID, as after 3...d5 White still has the possibility to play the Exchange with Nge2.
Agreed. I used to play both 3.Nc3 and 3.Nf3. There are solid and sharp lines in both openings, so it really does, I think, mainly come down to a matter of preference and it's nice to be able to switch off. I eventually gravitated to 3.Nc3, not because I liked it any better or any worse, but because of how it fit with the rest of my repertoire, and in particular my lines against the QGD and the Benoni.
Against the QGD, as MNb notes, 1.d4 Nf6 2.c4 e6 3.Nc3 d5 preserves White's ability to play the Exchange variation with Nge2. The 3.Nc3 move order also avoids a couple of sharp variations, such as the Vienna and the Ragozin, which are available to Black after 3.Nf3 d5 4.Nc3. Not that these need to be avoided, but it's more theory for you to learn.
Against the Benoni, 3.Nc3 c5 4.d5 preserves the option of playing the Taimanov or the Modern Main Line -- two of White's most testing lines. After 3.Nf3 c5 4.d5, White's options are more limited, and you can't even be guaranteed of getting the Modern Main Line, as an early Nf3 gives Black some additional options.
LeeRoth