I haven't done an audit of either but here are some points to consider:

1. Brave is built on top of chromium, so it "by default" exposes lots of new APIs that Google is introducing that make fingerprinting easier if not outright invade your privacy. For example see https://mozilla.github.io/standards-positions/ and look at the "negative" items. Many of them such as Web NFC, Web Bluetooth and WebUSB API are against because they don't have adequate protections against fingerprinting or other privacy or security concerns. Brave seems to do a pretty good job removing or disarming these APIs but they are basically trying to keep their balance on a shaky and antagonistic foundation.
2. On a similar note Google pushing these APIs work because of the greater market share. Again, derivatives can provide some resistance by disabling these APIs but unless all of them block the same APIs they will still be available widespread. So using a Chromium-based browser harms the entire web over time by allowing Google to have control. Right now Firefox (and derivatives) and Safari are the only browsers that you can use to truly oppose Google's control over the web platform.

Brave has tried one scam after another before. I wouldn't trust it for a second for any use.

Is it more private than brave? Normal Firefox: no Librewolf (Firefox Fork): yes Hardened Firefox: yes

As hard as it is for me to admit, and based on some tests, Brave had better fingerprinting resistance than Firefox. I don't trust the guys behind Brave, but their product is good.

Brave isn't more private than Firefox but depending on the platform that Firefox is on, Firefox might be less secure than Brave.

Not the point. Using a chromium browser is a vote for Google domination of the web. Just no.

Short version: Firefox on desktop, something chromium-based on Android. See https://www.privacyguides.org/en/tools/ for the long version!

By default? I think so.

https://privacytests.org/

(these test are done with browsers at their defaults). Librewolf is on par with Brave, but I vehemently hate its interface and refuse to unfuck it wasting my time on CSS.

I'm on Brave as well since 2021, after almost 20 years of being an avid FF user and supporter. I don't like how FF is evolving and what Mozilla is doing and I don't buy the "Chromium domination" argument. If the sole reason to use FF is that "it is not Chromium", well, the developers aren't doing a great job.

However, let's be real: privacy on a browser matters until you go to whatever website that track you on the server side (Google/Facebook/Youtube/Whatever), or when you write an email from from you Gmail account, or when you buy stuff on Amazon... And so on. Just use the browser that works best for you and don't be paranoid.

Brave is more secure, in terms of safety, because it's base on chromium and has unique Privacy Features. If you won't use Brave, LibreWolf or hardened Firefox is ur best choice.