Hey, real talk. You’re not choosing between two flavors of ice cream. You’re stepping into currents that are philosophically, spiritually, and energetically opposed.
Demonolatry sees demons as gods, allies, mentors. Solomonic magick sees them as hostile forces to command and threaten into obedience.
Before choosing books and a path, ask yourself: Do I want a relationship, or do I want control? Of course there is a ton more nuanced and overt differences between the two but in general this is one of the biggest differences.
If you don’t have enough experience to feel the difference between those paradigms yet, start slow. Pick one path and commit to it long enough to learn something real. Not for 3 weeks, like at least a year.
Do you have any experience with any occult paths to date? If so, what path? What experience do you have? Any religious background? All this matters and can help others give you better guidance rather than blurting out book titles they read 15 years ago. It will help us help you.
For Demonolatry, S. Connolly The Complete Book of Demonolatry is a good start. Her stuff is basic, entry level stuff and reading it will give you a perspective (not the only, or the best) on Demonolatry. Its enough to get started.
Regarding Solomonic, I dont walk that path but I hear there are a bajillion books on it. There are lots of folks that can help you with books to start out, or at least give you a taste of it to help you choose.
Good luck.