https://grapheneos.org/usage#web-browsing

Chromium and their particular fork have much better exploit hardening via sandboxing.

My understanding is Firefox has better anti-fingerprinting and uBlock origin via manifest v2 support (or v2 features ported to v3).

The argument often used is malicious ads. Sandboxing and hardening largely mitigates ads that contain exploits, but it doesn't protect against social engineering, crypto mining, tracking, etc.

So I guess it comes down to your threat model and desired experience.

I personally prefer the uBlock origin experience, but an ad free experience and escape from targeted advertising was my target opsec when venturing into privacy.