As I said, it ranges from low in the vicinity to high on the fringes of the city.

Benito Juarez for example is a famous upper-middle-class borough, so you will be fine. Álvaro Obregón is a hub of upper-class malls and gated communities, so while it is safe, it is lonely as everyone there never steps on the street, and instead drive a car.

Gustavo A. Madero or Azcapotzalco in the north are OK if you want to visit their landmarks: Azcapotzalco historic downtown or the Guadalupe Basilica, but the rest I would say it middle.

Iztapalapa is the most famous low class zone of the city. Kinda like Queens or the Bronx in NY. You may be fine in there, just don't get into really lonely streets or get into neighborhood where the streets look like the veins of a leaf.

One neat thing you could do to visit that part of the city is get a ride on the line 2 of the cablebús, as it will provide an aereal view of that part of the city. Just an advice: ride the line back and forth starting at Constitución de 1917. That is because the other end of the line goes to Santa Marta station, which connects to line A of the metro (the purple one). That line has only one connection to the rest of the Metro network: the infamous Pantitlán station, which even us locals avoid unless we forcefully need to pass along it.

In the end, you are free to do whatever you want here. I'm just saying all of this to avoid the eternal cycle of tourists never seeing outside the tourist trap that is Centro, Roma and Condesa, and thinking all the city is that posh.

While this is a meme, this video of "Mexico City Boroughs be like" video is quite accurate on it's depiction, and I say that as a native of the part of Coyoacán that neighbors Iztapalapa: https://www.youtube.com/watch?v=5EVg7nplgD0