Or prep books, honestly I’m just learning for what I can go through to best prepare me for the AP test and then have what I need for Multi variable in the future.
In general, any calculus text that covers AB will also cover the BC topics. So if you were happy with the AB text, use that. Also in general, no good single-variable calculus text will cover MVC, other than maybe a quick introduction.
For a specific recommendation for MVC, any edition of James Stewart’s Multivariable Calculus: Concepts and Contexts is fine. Stewart has also written texts that would be OK for BC.
For BC prep books, one is as good as the other, IMO. Barron’s or Princeton Review are both fine.
If you need free, here is a calculus book covering both single variable and multivariable calculus:
https://ocw.mit.edu/resources/res-18-001-calculus-online-textbook-spring-2005/textbook/
Looks like the Stewart calculus book can be gotten in a version with both single variable and multivariable calculus, or just the single variable calculus part, or just the multivariable calculus part.