Someone’s made a comparison of a few ROMs here.

Personally, I’d recommend GrapheneOS like the other commenters have here, but do your own research!

It has been a while since I’ve used it, but when I did it felt sluggish and missed some ads. It’s probably the only choice if you’re looking for something free though (besides 1blocker, haven’t tried that one)

Wipr 2 is a great paid ad blocker. Unfortunately most iOS blockers don’t work too well beyond this one and AdGuard (and I haven’t had the greatest experience with the latter either)

I’ve used Thorium (not as my main browser) and I like it. Decent privacy features, performance does feel better.

Some major downsides though:

1. It is not frequently updated to the latest Chromium patch; there have been times where Thorium has lagged three major versions behind. And just forget about getting patches that fix major security vulnerabilities until the next major update.
2. The browser is heavily opinionated, and while that has resulted in a browser with a half-useable version of the Chrome refresh, see this issue and it’s clear the focus is not on privacy.

If you want a browser that’s more focused on privacy and don’t care about the eye-candy that Thorium provides, the Cromite browser is only doing security + privacy patches, has toggles for more permissions, has V8 disabled by default, allows for automatic clearing of history, allows you to change the default referrer policy, has more chrome://flags, and actually gets updates frequently to the latest patch.

By default, sure. But uBlock is way more powerful when you configure it. Seriously, take a look at their wiki. I doubt that Brave lets you choose exactly which domains to connect to on a per-site basis. And do you really want an advertising company to make your adblocker? They’ve done shadier stuff.