Demons can be pretty tricky when it comes to this kind of topic. There are a few different categories that they could fall under: Fallen angels, demons, demon born, and grey areas.
Now to start off, the basic sense of a demon are usually evil. Demons are the most hostile type of spiritual entity that you could encounter. They tend to enjoy toying with humans to put it lightly, but are also greedy and tend to capture souls to make themselves more powerful.
"Demon born" is something that results from being the offspring of a demon. They tend to fall into a grey area since they are not entirely demon. There are two distinct types though. One that is "physically born" from the result of sexual intercourse with a demon. The other being a human that has a "fragment of a demon" left in them from a demonic encounter/possession causing them to become a human with demonic traits.
"Fallen Angels" aren't necessarily angels that were damned to Hell when siding with the devil after he rebelled. Rather they are angels that have fallen from grace. Because of this fallen angels can usually lean either way. They are one of the beings that can fall into either category.
Now the grey areas are a bit complicated. There are some demons and demonic creatures that don't entirely fit as either completely good or entirely evil. This can vary on the particular being though and normally doesn't apply to demons in the "hierarchy."