It depends what view you wanna take. I believe demons and angels are both very powerful beings. Some people believe demons are good, but some believe they are bad. Since I am Christian spiritual, yes I do believe in demons. I have felt demonic presences before.. they're not nice lol.. Demons, like said above, are pure spirit, like angelic beings, but opposite sides of the spectrum. There are higher levels, and lower levels spirits vibrate too. From what I know, I think, demons vibrate at a lower level, while angels vibrate at a higher level. Angels are pure light. Light shines in the darkness.
Hope this helps x