I believe that you are free to involve yourself with all sorts of beings, both light and dark, and that doing so is not only ok, but rather beneficial. I’ll tend to focus on either angels or demons for a time (I work with other spirits too, but generally speaking), and then occasionally switch as cycles of self-development begin and end.
I’ve evoked an archangel and a demonic king on the same day before. It’s only a problem if you make it one. The archangel Metatron even guided me to work with Lucifer. Their personalities may be rather different at times, but they all have your best interests at heart when you call upon them with a sense of authority.
I’d say do whatever feels right for you. You don’t have to “pick a side” or anything like that, and you are always the one in control, not the spirits. There’s something to be said for letting go of control at times, and the spirits aren’t going to wreck your life, but you are always free to make your own decisions.