In my personal opinion, toll roads and libres share two things in common. Some are good and some are bad, some you pay and some you don't. That said, I am finding that the libres are improving quite a bit.
We have been using the libres from Monterrey to Reynosa and Laredo. We find them to be in very good condition. Advantages are that they are free (not to us Mexican tax payers), have many stops along the way, excellent scenery and the same if not more security than the autopistas.
There are more offices for Policia Federal, municipal police, and military patrols not to mention checkpoints. More places to stop for good, homemade and economical food, gasoline stops, and promotes tourism in small towns. People talk a lot about helping los pobres mexicanos, well this a good opportunity.
In my humble and not very experienced opinion, autopistas present a false sense of security.