Safest cities in Northern Mexico?

I'm from Brazil, and I plan on visiting Mexico sometime soon. I've selected some places such as Merida, Mexico City, and Puerto Vallarta, but I've noticed very few recommendations for northern Mexico. This is a shame, considering I thought it might be a good idea to visit America afterward, and it'd be nice to have a last stop in northern Mexico before arriving there.

A bit unrelated, but this was also unexpected, as the HDI of these regions is higher, and they're also, as far as I know, the regions with the highest rates of European descendants, which are usually the locations colonizers treated nicely (at least in Brazil and the rest of South America). I'm guessing there's not a lot of Spanish structures and ledtovers in there?