A TN visa is better for the employer than an H1B. There's no application process, you simply show up at the border with your credentials, an offer letter, a letter of support, and $50 USD. It's not nearly as onerous as an H1B.
That said, a TN visa is worse for you as an employee. You are directly tied to your employer, and must leave the country as soon as you no longer work for the employer. It cannot be transferred, must be renewed every 3 years by exiting and reentering the country, and has no route to a green card.
Personally, as a Canadian engineer, I prefer TN visas since I have no desire to obtain US residency or a green card. My Canadian friends that are down in the Bay Area have been trying to get a green card for nearly 7 years now.
I didn't know that Mexicans were eligible for the visa though? I mean, I know it's tied to NAFTA, but the US & Canada like to exclude Mexico from a lot of those things.