If I'm the NFL, I'm taking the broadcast network that bids the most money. Everything else is noise. NFL owners want their money. Its also too political to choose favorites. Zero controversy is best -- you gave me more money, congrats! Hey other guys, you all have a shot next time, we don't play favorites -- just bid the most and its yours.

Don't play favorites, invite everyone to the party and let them fight over the last slice of cake.

Edit: OK but in the spirit of the question, I think NBC is the worst, but its not really about their NFL coverage, they do the same thing with most sports in that they try to create a "story" about things happening on/off the filed rather than keeping their focus on the game or sport. All the networks do this to a degree, NBC is the worst offender