From the official GOS account on Mastodon:
The only other browser [besides Vanadium] we can currently recommend is Brave. It preserves most of the security of mobile Chromium while adding more state partitioning, anti-fingerprinting and the most advanced content filtering engine. Vanadium is more secure but needs to catch up in those areas.
https://grapheneos.social/@GrapheneOS/111966180001152300
There are lots of reasons that some folks might dislike Brave.
Private company, runs an ad network, crypto, AI.
But there's no perfect browser out there. Brave is one of the least bad choices, per the GOS account:
If you rule out Brave then there's no mobile browser alternative to Chrome or Edge we can recommend due to lack of basic security.
https://grapheneos.social/@GrapheneOS/113948398641752397
Also, about Firefox and variants:
Firefox doesn't have a basic content sandbox on Android, let alone site isolation, and it has a lot of other security deficiencies.
The browsers referring to themselves as hardened Firefox variants only harden privacy, not security, and in fact most bring more security issues.
This applies to the Tor Browser too.
https://grapheneos.social/@GrapheneOS/111969790767423663