So what you mean to say is
saver awards are capacity controlled -- you can't get seats on all flights at all times. They are, however, the only way to get an award on non-UA airlines. Standard awards cost twice (or more) the number of miles, but they are good basically on any UA flight as long as there is space. You can't get awards on UA's partner airlines, though, using standard awards. There are other differences as well, but this is the basic distinction.
I mean to say:
"Welcome to FT!
You've really got two questions here, saver vs. standard and UA vs. NWA.
I can't speak to the latter. About the former, saver awards are capacity controlled -- you can't get seats on all flights at all times. They are, however, the only way to get an award on non-UA airlines. Standard awards cost twice (or more) the number of miles, but they are good basically on any UA flight as long as there is space. You can't get awards on UA's partner airlines, though, using standard awards. There are other differences as well, but this is the basic distinction."