I found this interesting article regarding the password vs. passphrase debate.
https://proton.me/blog/protonmail-com-blog-password-vs-passphrase
The takeaway is basically, given that the password is actually of considerable length, it doesn't matter which one you use.
However, if it's a password that you'll need to remember, it's probably better to use a passphrase. The master password for the password manager you use is a good example. (That's one password it can't remember for you.)