These two variations are very popular so which do you prefer? This is the Dragon Variation:

This is the Najdorf Variation:

Seems to me that there is only a pawn difference between these variations and I have noticed that many players play both a6 and g6 one after the other anyway.  Not sure what the crucial differences are.  I tend to prefer the najdorf but only because I am more familiar with it but then I usually play white in this position so it probably doesn't matter for me.

Yes they do usually play them one after the other but which one you do first really matters.