All I can say is there's realism and there is REALISM. AMSO is realistic to those who would consider the Spaceshuttle Mission 2007 SIM realistic. It's realistic to point of being usable/playable and there is and always has been a definite emphasis on graphical prettiness which people always find impressive.
NASSP on the other hand goes for REALISM, the problem is this level of realism is going to be too much for somebody looking to make a casual dip into Apollo in the orbiter environment. I'm sure I speak for most NASSP users when I say, we have been studying Apollo for years and simming it with the vAGC/Orbiter/NASSP and we all still have so much to learn.
AMSO and NASSP are not competitors but are complimentary projects. The vast majority of people may not have an interest in the most detailed realities of Apollo. Many people may want to experience the (virtual) thrill and journey of a voyage to the moon without having to concern themselves with P52s, REFSMMATs and PTC rolls. For those that enjoy the minute details there is NASSP

It doesn't matter which you use, as long as you are enjoying it!