I finally found where the best street food is located.
Instead of walking around randomly searching like an idiot, I actually thought about going to the busier places during rush-hour (where people are mostly to be walking around on their way to buses or the Transmilenio) and found that some of the best empanandas are very close to where I work ( a big bank tower that holds a ton of people).
Normally, you can find empanadas and arepas anywhere and anytime, but most are just sitting in a box all day and then reheated when you ask for them. These are kind of gross, not fresh at all, and don't taste good.
The best empanadas are sold by guys who sell them on bicycles that convert to street stands, they keep them in a cooler (or heater in this case) and serve them out of the box. It's funny that these guys look sketchy but their food is so much better than the restaurants and stores close by. My theory is that they cook them at home or at a restaurant close by and sell them where the most traffic is at a very cheap price. A good business plan, although I doubt they make much even though they're always packed.
However, the very best street food, and this makes a lot of sense when you think about it, is close to universities.
You can get all kinds of different cheap foods with some unique ingredients. Recently being a student I know its the same everywhere. We like salty, greasy, hot foods at the cheapest prices (sometimes we'll splurge a bit for the most popular chicken, CANES!).
It was the same on High Street back in Colombus. Every block there were 2-3 fast food or fast casual restaurants.
In Colombia close to the universities, they use all kinds of different ingredients, trying to draw more students in, and for what you get its a great deal by how low the prices were.
To recap: if you want a taste of the best street food cheaply and quickly, go where all the students are.