I have the Nav in my '09 Chevy and it is a love/hate relationship.
It was a $2000 option back then so for $700 now, that is more like it.
The graphics on the new Nav is 10 times better than their old (mine) units.
The MyLink on the '14 is nice. However you can't get it on the HD's until '15 model year.
I have OnStar on my '09 so if there is any question I just call them and they download the info directly into the radio. That in my opinion is worth it.
I like factory because you get a large screen and when I am driving down the road I don't want to have to strain to see a little picture.